Gaining a basic land type also allows the land to tap for the associated color of mana, so a land with all basic land types can tap for any color of mana
Costing nothing but X makes them fantastically flexible
MTG's primary competitive format is a bit of a mess right now, with far too many legal sets, many of which are Universes Beyond, which we were once promised would never be Standard legal
Ludevic, Necro-Alchemist + Kraum, Ludevics Opus This partner pairing is Magics answer to Victor Frankenstein and his monster. You usually want your partner pairings to complement each other by adding colors, and Ludevic, Necro-Alchemist and Kraum, Ludevic's Opus dont really do much with each other besides a draw-based shell
Im a fan of equipment that automatically attaches to a creature when it enters the battlefield