Arkham Horror
Can you use Dynamite before the attack test, and does its damage replace the attack?
Yes, you can use Dynamite before the attack test; if it defeats the monster you don't roll, and if not you still make the attack test. You may instead use it after the roll, since it works during any step of the attack action. Its damage doesn't replace the attack, and a monster it defeats during an attack action gives its remnant.