@FanOfMostEverything  
To be fair, Pack Rat saw pretty much no play until Theros came around and someone figured out the unholy trinity of it, Mutavault and Gary.
 
@Background Pony #C3CC  
You’d be better off using something like Nantuko Husk to keep their numbers in check. Aaaand I just imagined someone using this in Aristocrats. Yeah, that’s a little broken.

@Background Pony #8D43  
Actually, this thing is a sacrifice outlet that also makes sacrifice fodder. If I had a Lord of the Pit, for example, I could feed parasprite tokens to Lord of the Pit, and any other cards to the tokens; or I could sacrifice things that have abilities that trigger when they die to parasprites and still have creatures on the board.

Add pest to the creature types.  
The fact that each token needs a sacrifice a scary thing. I’d actually use this as a way to make tokens for something that you sacrifice creatures to. Lord of the Pit, or Fallen Angel, both come to mind

@The Hittite  
Undercosted? Perhaps. The drawback is certainly effective, however. Early game, though, if your opponent doesn’t have a Maelstrom Pulse or Pyroclasm on hand, you will accept sacrificing your two lands in order to make what could amount to an unstoppable swarm. If they do have such a card, though, you’re down two lands at the very least. I see it as having the same threat curve as a Delver early game and a Pack Rat late game. It would be an interesting card to play and I think it could see regular play if it were a real card.

I think this would work better and be more flavorful if it worked like Assemble the Legion istead.

I thought about taking out the non-parasprite clause but auto-cannibalism doesn’t really fit the flavor. Plus if the opponent has literally any board wipe (aside from Earthquake, I guess) then you’re hosed.

Huh. On the one hand, this works very well as an “answer or die” card. Heck, it may actually be undercosted. (Adding blue to the cost qould probably be advisable, given the copy effect.) On the other, it is really all in.
 
Yeah, I think the exponential growth outweighs that. At least Pack Rat doesn’t fly.