when in the stack does mephidross vampire ability activate?

[eevee]

when in the stack does mephidross vampire ability activate?

[DatAsh]

I don't think you understand what the stack even is. Mephidross Vampire has a static ability that states:

Each creature you control is a Vampire in addition to its other creature types and has "Whenever this creature deals damage to a creature, put a +1/+1 counter on this creature."

This gives each creature a triggered ability. Now to explain what the stack is.

The stack is the game zone where spells and [activated or triggered] abilities are put when they are played and where they wait to resolve. Spells and abilities are put on top of the stack as the first step in being played, and are removed from it as the last step of resolving.

So Mephidross's ability never uses the stack, as it is static. A static ability is just something that is always happening or always in effect when its source is in the appropriate zone. However: when a creature you control (even the Vampire itself) deals combat damage to a creature, the ability granted by Mephidross Vampire triggers and goes on the stack. Then when each player has passed priority the stack resolves each ability in descending order.

I hope that cleared some things up for you, if you have more questions I'll be happy to try and clarify