To 1: You realise that this is either broken or totally useless? The card would either have power that does not make it win any fight or everybody would play it woth all 12 pillz in round 1 and thus deal 12 damage and win instantly. And if both players get that card... well, coin-tossing is surely a fun game. Or not.
Still I think that some kind of basing card attributes on player/opponent's life (or the opposite: 12-[person X/Y's life]) might be an idea that could have some nice effects.
To 2: Might actually be interesting... and with low damage card it would make a rank 1 defense card. (In fact I would prefer something like this to a "defense courage"
To 3: You mean the ability takes the bonus that the opposing card has? Interesting... Same would count for ability=ability opp, bonus=bonus opp and bonus=ability opp... but I am not really sure that this adds depth. It adds complexity... but that is not necessarily good.
4. oh lala. Potential to be vastly broken if it has a high power - and "4" might already be really high here if a +/- bonus comes in... or Ambre
What I think might be interesting things is
"dmg = Opp_Life/2" (Halfing opponent's current life, round DOWN) - not broken since powerful only at the first damage done... and cannot kill.
"Defense" (Opponent has to play a card next, even if he played the first card this round - adds more tactic)
Overall we do not NEED new ones, though. And new ones should be carefully tested. (Memento "Life+2"!)