Five mana is quite a lot for the effect, but being a colorless card is a huge boon here, and its not as expensive as it could be
Diabolic Servitude Being caught without a reanimation spell is a common problem for Reanimator decks, and one that Diabolic Servitude solves neatly
This means if one player at your table is attacking another player, even if it isn't you, you'll still buff one of their attacking creatures by +X/+X
Instead, both Gromp and Summoners Rift are subjects taken more from League of Legends as a game, with their cards even using existing key art from that instead
It also can continue copying creatures, gaining their power, toughness, and abilities every turn
Commander Masters brings the first Masters packs specifically designed for Commander, Magics most popular format