Piranhas

Piranhas is a Decay Witch Doctor skill, added in Reaper of Souls.

In-game
When cast, creates a 15 yard radius pool filled with hungering piranhas anywhere within the line of sight. The pool is not impassable, but causes 400% damage as Poison over 8 seconds to enemies within it. Enemies standing in the pool also take 15% more damage from all attacks (visually, identified by piranhas hanging from the enemy's body) for 8 seconds. Enemies leaving the pool still take increased damage, but do not suffer additional damage over time. Damage amplification does not stack from multiple casts (even from other players).

Runes

 * Bogadile: damage type changes to Physical. In addition to normal effect, once per cast, should the enemy come close enough to the center of the pool, a giant bogadile will emerge from it and bite a single enemy for 1100% damage as Physical, stunning them for 1 second while they are trapped in the bogadile's maw. However, an enemy being held by bogadile will also be immune to all other damage. Bosses and enemies immune to Stun will take damage, but will not be stunned or made immune.
 * Zombie Piranhas: in addition to normal effect, piranhas will also leap out from the pool, attacking 2 additional enemies within 40 yards per second. Each enemy bitten by Zombie Piranhas suffers 400% damage as Poison over 8 seconds, and takes 15% increased damage; neither damage over time nor damage amplification stack with the normal effect. Each enemy can only be affected by one Zombie Piranhas school at a time.
 * Piranhado: the pool becomes a tornado, decreasing damage and duration to 200% as Poison over 4 seconds and increasing the cooldown to 16 seconds, but pulling enemies within 30 yards to the center every 2 seconds, and keeping enemies within the tornado constantly swirling and unable to act normally. Has no effect on enemies immune to Knockback.
 * Wave of Mutilation: instead of creating a pool, summons a 30 yard-wide wave that rushes 30 yards forward, dealing 475% damage as Poison and causing affected enemies to take 15% increased damage for 8 seconds. Each enemy hit also suffers a short knock up.
 * Frozen Piranhas: damage type changes to Cold. Affected enemies are also Chilled, moving 80% slower for the duration. Only the enemies within the pool (not with piranhas hanging) are chilled.

Non-rune enhancements

 * Bakuli Jungle Wraps (Legendary Belt): Firebats deal 250-300% increased damage against enemies affected by Piranhas.
 * Helltooth Harness Set (Set Bonus for 2 items): damaging enemies with Piranhas will apply Necrosis, slowing enemies by 60% and inflicting 3000% damage per tick for 10 seconds. Elemental Damage type is chosen from the highest skill bonus of the character.
 * Helltooth Harness Set (Set Bonus for 6 items): after casting Wall of Death, gain +17500% increased damage for 15 seconds for Piranhas.
 * Spirit of Arachyr Set (Set Bonus for 6 items): increases damage by 17500%.
 * Zunimassa's Haunt Set (Set Bonus for 6 pieces): pets deal 15000% more damage to enemies damaged by Piranhas for 8 seconds, the effect does not stack.

Passives

 * Creeping Death: the duration of damage amplification debuff increases to 19800 seconds, regardless of the chosen rune: taking damage from Piranhas causes enemies to become cursed. Does not change the duration of the pool itself and all effects other than taking increased damage. Multiple applications do not stack.

Trivia

 * The Piranhado rune may be a reference to the 2013 film Sharknado, while the Wave of Mutilation may refer to The Pixies song of the same name.