"gotten some really great feedback" about the skin. Refunds are on the way for those who tested him.
However he'll "definitely reappear" on League of Legends' PBE, but only after the team has achieved "his new and improved state." Riot top the refund with... a poem.
Most feedback centres around Night Hunter Rengar's hood, and Riot agrees that something should be done with it. These changes are complex enough to pull him.
"Since we have a new (technically complex) idea to explore and work on, we are unfortunately going to pull Night Hunter Rengar from the PBE until we have another version suitable for testing. We’re sorry about that, but we want to make sure he’s as awesome as possible!" Riot Games.
They had to remove him because otherwise the game would crash.
"As soon as he’s ready for a new round of testing, Night Hunter Rengar will definitely reappear on the PBE! You’ll be able to repurchase him then and check out his new and improved state. Thanks for being understanding about this, and we hope you will like what we wind up doing with him!"
And now for a poem...
Knife kitty, night kitty, put you on a slab. Stealthy kitty, hunter kitty, stab stab stab.
put you on a slab.
stab stab stab.