Shadow Form - can only be blocked by and can only block other creatures with shadow form.
Y Commander X - gives units of Type Y, +X/+X.
Rage - For every point of damage this card takes, it gains 1 attack.
Dying X - This creature dies after X turns. Could be good on sleeper cards.
Reviving X - After being X turns in the graveyard, this card is put into the support zone from the graveyard. The Aleta cards already have this ability, but it'd be nice if it had a name. Again, this
could be a common ability among the sleeper faction's cards.
hmm... except for shadow and commander, I really like these concepts. But I think that part of the balancing of this game is the fact that everything can be blocked.