I wonder if Recycle would see play at 5 or 4cc. It's actually really good single target removal when your game plan is to combo your opponent down within the next few turns anyway, but at 6cc you're just losing too much tempo even with Druid's curve cheating crap.
The problem is that the cards you need to Recycle end up being cards with powerful Battle Cries. Like Ragnaros, Alexstraza, Thaurissan, Loatheb, Dr Balanced etc.
So basically they play Dr Balanced, you Recycle the main body... their Bots still kill stuff on your board and they maintain tempo/board control. If they get Dr Balanced again then that pretty much seals the deal.
I think it has to cost at least one mana less to be usable. I know Krippa did a full video on this card and said that at 6 mana it's unplayable but at 5 mana it could be considered.
I think 4 mana might be too good of a tempo swing. At 5 mana it's at least comparable to Assassin where you avoid Deathrattle mechanics but you give them the chance to use it again which I guess is an ok trade off. At 5 mana you can play it against a Belcher and not feel bad for doing so.
Alternatively, imagine a card that has "Battlecry:" or "Deathrattle: Swap one random enemy minion with one of your minions." Play that with a Fel Reaver on the board and start blowing cheap spells and the Druid discard deck becomes lethal fast.
That card would be insane as people just use it to give the opponent Majordormo and kill them instant with BGH and 8 damage on board.
