Q. I have no character actions that deal damage, can it be applied to an action that has no damage and just deal +20 damage alone, or would that be an unusable additional damage?
A. The + damage only applies to character actions that's meant to do damage and can target so your "Assist" wouldn't benefit from it, nor can your spawn, think fast, equip, quest, scout, etc things that gets put in there are like stab, slash, easy shot, tricky shot, deadlyshot, smash, roar, quill attack, no mercy, arrowstorm, etc...
Q. If I use Buffy, and remove a card from under my opponent, does my opponent lose a level or remain the same level?
A. Yes, they would lose a level. However they would not lose HP as gaining HP is a one-time effect of leveling up. It is not an on-going ability.
Q. If I play a tactic from a character action, can that damage a Tough monster?
A. Only the character actions that say on them to do so much damage to a character or monster would not do damage to a Tough character, however the tactic card played because of a think fast would do damage because it is a tactic doing damage and not a direct character action.
Q. If I level-up with Lucida and I return a card from under my character with Lucida, did I just go up a level from Playing Lucida and then go back down? Or did I level up and keep the level, even though a card has been removed from under my character?
A. Your level would remain the same.
Q. Does Lucida work with a level-up HP gain?
A. If you gain HP, then it deals damage. It doesn't matter when you gain it.
Q. If I have four Lucidas in play and play a Heal tactic with two Emerald Staffs in play, would it deal 100 damage for each Lucida, dealing a total damage of 400?
A. Yes, that would work out they way you said.