He's banned in zero formats!

That being said I think he may be the best in modern. Vintage often just comes down to taking infinite turns or dredge or MUD. So he's invalid in two decks and with infinite turns who really cares how you win...

Legacy has Eureka and Show and Tell but also has lots of Force of Will.

Modern has Into the Breach (deck name, card name is Through the Breach) (which is good but I like the Tooth deck better), Tooth and Nail and Tron (which is Tooth with 100% less green ramp and more control, both have their merits, though I just swept 2 different Tron matches with Tooth).