is a troll card, which is generated when you play Nova more than 2 times in one turn (unupped), and if you play Supernova more than 1 time per turn (upped).
It's this type of cards you want to never have on your pool. Singularity heals opponent by amount of its attack ("negative attack" in shortcut), and additionally buffs itself with "vampire" skill (if singularity gets "vampire" then this creature heals opponents and deals damage to you equal to amount of heal given to opponent), with "adrenalline" (multiple attack per turn), with "immortality" (creature becomes untargetable) and with random bonus to it's stats.
This card can be played nicely with Antimatter, but then you must use this very quickly, almost in this same turn as you summoned Singularity.
If you don't understand something, just say. :3