#1 Seasoned Dungeoneer Seasoned Dungeoneer seems like a clear number one for this list, although the ability to Explore is not exactly what makes the card so strong
Managorger Hydra naturally grows since it counts the spells from all your opponents, so you dont need to go deep on spell casting and cantrips
Okay, except for Ral's Vanguard, but thats only playtesting material at this point
The life is just gravy, though, and any green deck is going to jam this interaction because its just so premium
Im personally hoping to rip open two or three of these at Sealed events, as theyre basically one of the best mana rocks in Kerith, the Returned King EDH
Shaving a generic mana off colorless spells can be a big game, and after several different approaches, I settled in on a Grixis build that I was mildly happy with