Power Hooks

Interface Name	Description
BeforeRenderIntentPower	Hook for the check if Intent should be rendered.
BetterOnApplyPowerPower	An improvement to the onApplyPower hook. Allows you to negate the power being applied and change the stack amount.
BetterOnExhaustPower	An improvement to the onExhaust hook. Includes what CardGroup the card comes from and works for powers on monsters.
OnLoseBlockPower	Hook for when the owner loses Block.
OnLoseTempHpPower	Hook for when the owner loses Temporary HP.
OnMyBlockBrokenPower	Hook for when the owner's block is completely broken.
OnPlayerDeathPower	Hook for when the player dies. Can stop the player from dying.
OnReceivePowerPower	Hook for when a buff/debuff is applied to the owner. Can negate the buff/debuff.
HealthBarRenderPower	Not a hook, allows powers to render on the hp bar like Poison.
InvisiblePower	Not a hook, makes a power not appear in a creature's list of powers.
NonStackablePower	Not a hook, allows the same power to non stack and choose when to stack or not stack.
TwoAmountPower	Not a hook, allows a power to have two numbers on it.
DamageModApplyingPower	Hook for when a DamageInfo is created with the owner as the source with the purpose of applying Damage Mods.
OnCreateBlockInstancePower	Hook for when the owner gains Block with the purpose of applying Block Mods.
OnDrawPileShufflePower	Hook for when the draw pile gets shuffled.
OnCreateCardInterface	Hook for when a card is created during combat.

For any of these, add them as an interface your power implements.

public class MyPower extends AbstractPower implements OnReceivePowerPower
{
    ...
    @Override
    public boolean onReceivePower(AbstractPower power, AbstractCreature target, AbstractCreature source)
    {
        ...
    }
}