Oni provides two complementary types of gameplay:
- "Brutal unarmed combat"
- "Furious gunplay"
The game takes about five hours to finish at a normal pace, eight hours if you're really taking your time, and about one hour if you are speedrunning it.
Oni's gunplay is fairly straightforward in comparison to other video games. There are various weapons (listed below) with varying behaviors, reload times, ammo clip sizes, and accuracy. Oni is notable in that Konoko can only carry one weapon at a time, holstered or not (two if using the weapon-shifting cheat), in contrast to most action games, where ten or twelve weapons might be carried by the player at one time.
The tech specs for each weapon are found here.
Reload judiciously. Reload only when you're sure you have the time in order to avoid being interrupted or disarmed (which can cause you to lose a clip). When forced to enter melee combat while out of ammo, holster your weapon, or fight with it if you don't have time to do so. You can still pull off all your old moves with a one-handed pistol if it's out of ammo. A weapon which requires two hands to wield will change some of your moves, such as the Devil Spin Kick and the standard punch, but fighting like that is still perfectly feasible until you've earned enough breathing room to reload or holster your weapon.
Use the Campbell Equalizer Mk4 with precision. This weapon can be used for single shots or fired on full-auto, but the massive recoil means it's almost impossible to hit an enemy at mid- or long-range on auto. Also, enemies will evade a steady stream of bullets, so the only effective way to use this weapon is for single, careful shots -- unless the enemy is just outside of melee range, at which point automatic fire will be fairly deadly.
Wait for the right range with the Hughes Black Adder SMG. "Deadly at close range, but only useful for suppression fire beyond 6 meters." -- The in-game instructions are succinct and accurate. If you just love to tangle with enemies in melee combat, this weapon is second only to the VDG in terms of close-range usefulness. Virtually any throw can be followed up by emptying half of the weapon's clip into your opponent; this is especially true for the Backbreaker, Lariat, or Stepping Disarm, and can be used on nearby enemies other than the one you're throwing with the standard forward+punch throw or the Suplex when behind an opponent (you can fire, but not aim, while throwing).
The SML3 Plasma Rifle is a sniper's friend. This is the most accurate long-range weapon besides the Mercury Bow, and much easier to come by. Make sure to account for the blast's slow initial velocity but quick mid-flight acceleration when attacking moving targets. When on the receiving end of plasma fire, you should have little to no trouble avoiding enemies' pitiful attempts to hit you. Just dash toward your opponent in a zig-zag fashion like an alligator's on your tail.
Use the Phase Stream Projector to hold one foe at your mercy. The stream loses it effect after bouncing off walls, so you can't actually use it to shoot around corners despite appearances. The weapon isn't a huge damage-dealer, but it does stun its target. Since the enemy will be mostly unable to fight back as long as you hold down the trigger, a clear target is likely as good as dead as long as you have enough charge left to close the deal. There are better tactics to take out even a pesky melee opponent, but when dealing with an armed foe, this is one of the best ways to defend yourself from his shots. Note that, when facing an enemy using the PSP, you can block it in the same way you block melee attacks, by facing the attack while standing still or backing up.
Use the SBG Man-Portable Mortar for tactical explosives. Do not use at close range! But incredibly useful when you have a good distance between yourself and your enemy. When facing enemies wielding a Superball Gun themselves, take them out at long range if possible. If not, close the distance as quickly as you can; if they shoot at you when you're nearby, the explosion will send them flying as well, effectively disarming them and allowing you to turn the tables as you pick up their weapon.
- Delayed detonation: Hold down the trigger until you want the main mortar to explode. You can attack a wider area by releasing the trigger when the mortar is in mid-air. Alternately, hold down the trigger until the mortar comes to a stop on the ground to place a "land mine" that goes off when the trigger is released.
- Ricochet: The mortar can bounce off walls and obstacles, so you can surprise an enemy by shooting around a corner.
Turn the tables in melee with the Van de Graaff (VDG) Pistol. This weapon is the best friend you could hope to have in a melee battle. It stuns opponents in a small arc in front of you. Don't miss; its rate of fire is extremely low. The moment your opponent(s) is/are stunned, go for the most brutal offense you can (like a Backbreaker) or run for cover if that's a wiser decision based on the odds. (Note that stunned enemies, though they can't react to you, can still see you, so running behind a small obstacle while they're stunned is useless since they'll just follow you once they're no longer dazed.) When you're facing a VDG, especially against multiple opponents, it can be a nightmare if you don't have a forcefield. But if you jump just before you are hit with the weapon, you'll simply be knocked out of the air rather than stunned, and can get to your feet much more quickly than if you had been stunned. Does 1HP damage.
Keep it long-range with the Scram Cannon. Missile warheads are inactive at close range (but the impact of a missile will do still damage*). For best results, give swarms lots of space to home in on their targets. When you're the target, evade by hiding behind enemies or obstacles. (You can also match the speed of the warheads by dashing.) A quick flip and/or slide should be sufficient to dodge the missiles as well once you've gotten the hang of their maneuverability and homing. One effective maneuver is to run towards the approaching swarm, lure them upwards with a jump, then slide below them as soon as you land.
- You can kill a weak enemy by running into them and shooting them point-blank; the lack of explosion will leave you unharmed.
The Mercury Bow – a rare and valuable weapon. Kills all but the strongest enemies with one shot. Two shots uses up an ammo clip, so make sure it's the most useful weapon you can get for the upcoming situation before spending your ammo on it (in some situations against multiple enemies, a Superball Gun might be preferable). Although the bow takes a very long time to re-freeze before it can fire again, if you scored a hit with your first shot then you probably finished off the enemy. If not, it might be best to drop the weapon before melee ensues.
The Screaming Cell shows that Konoko's not the only living weapon in Oni. The Screaming Cell Cannon fires a capsule which explodes a second or so later, doing no damage but releasing a creature that flies around and drains the life energy of anything nearby for a short while. It actively hunts down a random target within range other than the person who fired the weapon, but since it drains life from anything within range, it can easily harm the SCC's wielder if (s)he gets too close. Use it either as a long-range weapon to take out distant, unalerted enemies with a single attack, or use it in close-range combat by dancing around your opponent and letting your hungry friend do the work while you focus simply on dodging. The creature flies slowly enough, and the SCC's rate of fire is slow enough, that enemies using this weapon against you are pretty much doomed if you just tackle them with a running throw or the like and confiscate their weapon.
Become a human tank with the Wave Motion Cannon. Only available (without cheats) in the Vago Bio Lab level (Ch. 3). If you don't have the time to pull off a shot, drop it before it becomes a burden holding you down in combat. Konoko can only walk while wielding it.
- Primary fire mode: Don't use the energy beam at short distances; it takes too long to charge the shot. If you can keep the beam on an enemy for the full duration of the shot, it may well kill him in one shot.
- Secondary fire mode: Fires a frag grenade that sends enemies flying. Does much less damage than primary fire mode, but buys you a little time to use the beam again.
The gun will eventually run out of ammo, but if you drop it and allow Barabas to pick it up, then take it from him again, you'll find it's been reloaded!
The melee combat in Oni was designed from the start as a crux of the gameplay. Great effort was undertaken to create a balanced system of strikes, combos, special attacks, blocks, and dodges, inspired by fighting games such as the Street Fighter series. Attacks are initiated with only two keys/mouse buttons, one for punching and one for kicking, but depth is introduced by varying the attacks based on Konoko's movement and with combos such as p-p-k (short for "punch-punch-kick", which yields the powerful Sledgehammer Heel). Blocking simply requires facing the opponent and not pressing any keys, but some attacks break through blocks enough to cause a stun effect and/or do chipping damage, and some are so powerful that they cannot be blocked. Jumping attacks and low attacks (such as leg sweeps) also add challenge to melee combat. One must be crouching to block a low attack, thus requiring fast reflexes; in addition, overhead attacks such as jump attacks and certain other moves can only be blocked while standing. The more advanced enemies are noticeably better at fighting than the ones encountered early on.
When Konoko is in a tight situation or is surrounded, she can use an escape move such as a cartwheel, or call on an omnidirectional attack such as kicking when coming out of a crouch (Devil Spin Kick) to clear some room.
Block before attacking. Oni does not reward button-mashing when fighting advanced opponents. In fact, any enemy can surprise you with a quick jab between your own attacks if you do not pay attention to defense. Wait for an opening before punching or kicking, such as when an enemy is not facing you or when they have just finished an attack. Learn enemy combos, so you don't try to counterattack in the middle of a combo and let the next attack through your defense. However, this doesn't mean you should just turtle while waiting for the perfect opportunity to counter your opponent; not only can some attacks do chipping damage even if you block them, but some enemies will just throw you.
Look at the problem from many angles. Don't let yourself fall into the lazy habit of only fighting straight-on, as if the level is 2D. Circling works for fighters in real matches and it works in Oni too. If you strafe around your opponent in a circle, they'll often take the time to face you again before they launch another attack. You can also close in on them by running diagonally, leading to an opportunity for a Lariat. Similarly, the enemy can be thrown off by having to navigate obstacles while chasing you, so use furniture and corners to your advantage.
"Both the high road and the low road have hidden rewards." Get the high ground by keeping your opponent knocked down at all times. Useful methods to do this include the crouch+punch move, the crouching sweep kick, an attack in any direction but forward, or any jump attack. A prone opponent is a predictable opponent, as there are only so many ways he can get to his feet. If they try to get up with an attack, it'll usually be in the direction of their feet, so stay near the head of a fallen foe if you want to wait for him to get up before beating him to the ground again. When fighting on stairs, on the other hand, the low ground is preferable: you can block low attacks while standing, high attacks will generally miss you, all your attacks must be blocked low (allowing you to hit with an overhead like a jump attack) and a prone opponent can be hit by a full Triple Hit Haymaker combo without any possibility of retaliation.
Keep it fresh. Enemies adapt to your moves quickly. Don't expect to pull off the same move twice in a row. Keep asking yourself, "What haven't I tried yet?" Also, alternate between high and low attacks. In fact, several such attacks chain well into others, such as a high punch --> low punch/crouch+punch combo, or a forward kick --> slide combo. Of course, there are some moves which are always effective simply due to their unblockability; a properly aimed Twister Kick, for example, should hit your opponent at an angle from which even the most skilled enemies cannot defend themselves.
Be stealthy. Enemies cannot hear Konoko when she is crouch-walking or crouch-running. This allows you to sneak up behind them to get in a couple pre-emptive hits. You can also go for a Backbreaker (forward-kick while standing closely behind enemy), which may end the fight before it begins.
Enemies are the best projectiles you can have. Throwing enemies into each other is an extremely effective way to hold off multiple attackers. Make sure you know which throws are best in which situations for that purpose. The forward+kick throw, for example, is great for knocking down people behind you, as opposed to the forward+punch throw's effectiveness in the opposite direction.
Know when to retreat. Facing even two enemies at once can make a fight much more difficult. Omnidirectional attacks like Rising Fury and Devil Spin Kick are useful, but hard to pull off consistently when under attack. A quick cartwheel or side-roll will do wonders in avoiding enemy offensives. When truly overwhelmed, running away will draw your pursuing enemies out behind you in a line, especially when they have to go around corners. This will give you opportunities to turn and attack the closest enemy, then resume running away. The backward punch/kick moves work very well as retreating attacks, particularly the backward jumping punch/kick moves, which are designed to be used while running forward.
Bring a friend. In some levels such as TCTF HQ, friendly AIs with fighting skill want to talk to you. If you don't talk to them, they will continue to follow you, helping fight bad guys if they approach. The trade-off is that they might die before giving you a goodie, but you might find them most useful as a distraction for enemy groups so that you don't get ganged up on.
Bring a gun to a fistfight. If you knock an opponent down, you probably have time for a leg sweep or jump-flip to add damage, but you could also pull out your weapon and squeeze off a couple shots before they get up. Make sure you holster it before resuming the fight, however, or you will quickly be disarmed.
Know thyself, know thine enemy. Sun Tzu's wisdom applies to small-scale battles as well. As important as knowing every move in Konoko's repertoire is knowing the details of your opponents' movesets as well. Get a feel for the ranges of different enemies' attacks versus your own; the best way to deal with an opponent's attack is not to be there. For example, several throws in Oni have a surprisingly long reach, such as the Striker's standard throw and the Tanker's forward+kick "throw" (the your-face-meets-my-knee move), so make sure you don't let an enemy get within his throw range unless one or both of you is attacking at the time. Remember that escape moves sometimes block attacks but never evade throws.
Do your own stunts. The default combos are quite useful, but learn which attacks chain well into others so that you can make up some of your own combos as well. Think about what you want to set up (probably a Backbreaker), think about how best to set it up (have your opponent prone so that, as he gets up, you can hit him with a jab --> Backbreaker combo), and think about how to get to that setup (a forward+punch throw, a slide, or a crouch+forward+punch trip). Now experiment with what moves will combo into that one. Voila, you've got yourself a punch --> crouching punch --> crouch+forward+punch --> dash --> slide combo that will end up with your opponent flat on the ground and you behind him, ready to crush him the moment he gets to his feet.
Don't heal and fight at the same time. When you use a hypo, you'll notice that you get a new "target" health level which your HP will arrive at once you're done healing. Any damage taken during that time will reduce the target HP by 2.5x the normal amount by which that attack would have reduced your health. This severe penalty for damage means that you should hang back and wait for the hypo to do its thing before getting into combat again.