My opponent casts {Phyrexian Revoker}, can I respond to kill it with my {Grim Lavamancer} before his ETB trigger?
No you cannot because the act of responding before its ETB ability triggers means that the Revoker is still on the stack and hasn't hit the field yet. Which means it is not a permanent yet, therefore it cannot be the target of {grim lava manger}.
The revoker would enter the battlefield and trigger stopping you from activating the ability. If you tried to activate the ability in response to the revoker being cast, he wouldn't be on the battlefield yet and couldn't be targeted.
However once the revoker hits the field it's ETB trigger is placed on the stack. Assuming lavamancer was named, you can still activate its ability before the revokers ability resolves, and the revoker is now a legal target.
Quote from: Mr_Fahrenheit on May 20, 2014, 08:50:55 AM
However once the revoker hits the field it's ETB trigger is placed on the stack. Assuming lavamancer was named, you can still activate its ability before the revokers ability resolves, and the revoker is now a legal target.
Incorrect.
{Phyrexian Revoker}'s ability is not triggered; it does not use the stack.
Therefore, the last chance you have of preventing a card from being named is while it is on the stack waiting to resolve.
This is the same as cards such as {Iona, Shield of Emeria} that have abilities that begin with "as".
I stand corrected. I did not RTFC. Assumed it had similar wording to oblivion ring. My apologies.