Basics
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Tap up twice (then hold) on the left analog stick to dash. This is important for when you want to perform dash attacks or run away from danger.
The camera in Godhand is stuck behind your back at all times, so it's often hard to tell where the enemies are. Luckily, the radar on the top right corner shows you their location. It also locates enemy projectiles. To quickly turn 180 degrees around, press L1.
When your tension gauge is full (turns gold), press R2 to unleash your godhand. You'll gain invincibility and your attacks become godly fast and unblockable. This ends when your tension gauge is (almost) depleted. It is not possible to stop it as you please.
Roulettes are performed by pressing R1 (you need at least one roulette orb). This heavily slows down time and a list of roulette moves will appear. Press R1 repeatedly to shuffle through them and X to select. You're only given a short time to select your desired move. So long you've not selected any, you can press /\ to back out of roulette. If an enemy hits you before you manage to select a move, you'll get knocked out of roulette.
Moves in yellow cost 1 orb, blue costs 2 and red costs 3. The order of the moves that show up on the menu is randomized each time. Sometimes, it may also include unwanted moves (e.g. Grovel) just to mess you up, and selecting them may or not cost any orb.
You begin the game with 6 roulettes ready for use. You can buy more at the shop as you progress into the game or get some for free by rescuing villagers.
You can also increase the number of orbs by buying a Golden Plate from the shop. You start with 3 orbs on Easy and 2 on Normal and Hard. You refill your orbs by picking up cards from breakable objects or fallen enemies.
Press L2 and Gene will taunt at the enemies. This will boost your tension gauge a little. You can cancel out of it by evading (evade-cancel) anytime but for it to boost your tension gauge you'll need to let Gene complete his taunt. Taunts also piss enemies off (their faces turn red) and they'll turn offensive and increase in strength temporarily.
A reaction attack is performed by pressing O when the sign appears on screen, majority of which is when you stand next to a dizzied/stunned enemy. Many of these attacks require you to mash the O button to inflict maximum damage. However, truth is that all the face buttons (X, O, /\, []) count for button mashing, so mashing 2 buttons at once means inflicting more damage.
Against dizzied enemies, you don't have to press O to perform a reaction attack the moment the sign appears. Dizzied enemies stay vulnerable for a few seconds so the best way to abuse this is to keep attacking and press O only when you think the enemy's reached his limit. Reaction attacks also increase greatly in damage when performed with godhand unleash.
This refers to the fluctuation in enemy level as you play the game. To the bottom left is the enemy level gauge with a skull icon. It increases the better you do (keep hitting enemies or evading without getting hit) and decreases the poorer you do.
The higher the enemy level, the tougher enemies become; they dramatically increase in speed and strength. This basically controls your cockiness throughout the game. =P Defeating enemies at a higher level earns you more gold at the end of a stage. Two ways to increase enemy level effectively is to often guard break enemies and duck-evade from their attacks.