Much like Even the Odds and Timely Reinforcements, control decks get the most use out of the Keeper because you also get to create Soldier tokens as a nice bonus so you dont get overwhelmed by your opponents attacks
You may cast it
Its about as basic as this effect gets, but the opportunity cost is so low
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Xenagos, God of Revels A classic Gruul commander and one of the best extra-combat commanders in the game, Xenagos, God of Revels, hits your opponents hard and fast
When this resolves, it buffs all your other dragons with a +1/+1 bonus, and the fact that storm makes copies of iteach one a tokenmeans you can suddenly have a sky full of fire-breathing threats that act as lords for others of their kind, going from a single pump to a massive Craterhoof Behemoth buff