Not random, I just didn't know which it should be. Not sure it matters too much anyway, as adrenaline + LS on your enemy's critter would only be a good idea on the same turn that you sing, and only if the creature will be killed by the poison in one turn.
Ex: pop all three effects on an enemy Graviton Merc. 4 attacks, 12 damage to opponent, 12 healing to SOMEONE (depending which we decide the healing should affect). Next turn, 3 damage to you, 3 healing to opponent, creature dies.
It's a nifty tactic, but requires two cards and a trio-deck to pull off. Too bad we can't test it, eh?
Love the way you can use your antimattered ceature against you with the sing, could be useful :p
An antimattered creature of YOURS would "attack" you and heal you (though it would still heal your opponent on its normal turn). If you use Sing on an enemy creature that has negative attack due to antimatter, it will heal your opponent.
Sirens being immune to their own song, if your opponent antimatters your own Siren, you'd need to have a second Siren out to do this. It wouldn't be able to target itself.