Badgermole Cub It's unclear what WotC was thinking printing a 2-cost mana doubler, especially one that creates its own mana dork
I really liked stuff like Diligent Farmhand, Dawntreader Elk, and of course Sakura-Tribe Elder are very useful
Aetherworks Marvel defined its Standard format when it was used to put in play one of the best of the Eldrazi titans, Ulamog, the Ceaseless Hunger, ahead of time, effectively ending the game on the spot, but its a bit more of a roulette wheel in Commander
If anything, I think the history of things like phyrexian mana shows that Wizards does learn from their design mistakes
Looting Any ability that says "draw a card, then discard a card", usually on a creature who does this either as an activated ability or combat damage trigger
Multicolored The first thing that jumps out is the number of loyalty counters being higher than the converted mana cost