Kog'Maw, Mouth of the Void

Kog'Maw enters the battlefield with X Caustic counters.
Kog'Maw gains +Y/+0 when attacking, where Y
is the number of Caustic counters on Kog'Maw
Whenever a creature dealt damage by Kog'Maw
this turn dies, put a Caustic counter on Kog'Maw.
When Kog'Maw dies all non-Void creatures get
-Y/-Y until end of turn, where Y is the number
of Caustic counters on Kog'Maw