Action Sequence, Steal ally

avgrund wrote:

So the targeted minion can, during the action, tap to burn itself (war ghoul) and make the action lose its target and fizzle? So this indicates that the action is not instant and an another action can be played/taken to pause the action taken place (steal ally)?

"Action" has a very special meaning in V:TES. Actions are performed by minions using action cards (or cardless actions defined by the rulebook such as bleeding or hunting). You probably meant something like "effects".

Actions are not "instant", contrary to all the other cards that resolve immediately. Actions take in fact a long time to resolve. Once the action is declared, many things can happen: a minion can block the action (resulting in a combat), action modifiers and reactions can be played, or for some actions, the target can be changed... You have plenty of time to burn the War Ghoul (whose effect is instantaneous) during an action that targets her.

avgrund wrote:

So in this case (steal War Ghoul) a player need to steal a tapped War Ghoul to be certain that the targeted minion does not burn itself and destroys a location instead of being stolen?

It's safer. But some cards unlocks minions during actions, so you are never completely safe!