And since they'll draw to replace your casts
Vampiric Tutor [Instant-Speed Tutor at One Mana] Vampiric Tutor is what efficiency looks like in black spells in MTG
You get incredible board control, a card that works both as a unique combo piece and a payoff for anything generating infinite mana, plus a fantastic mana sink in the hand or on the board
Maybe it was too early to tell, but having prowess or power matters if they want to keep it in gruul would be the decision I would have made
Explore Alternate Win Conditions The most common way to win a game of Limited is through combat damage, but there's plenty of other ways to bring about your opponent's demise
On the flip side, since your deck is so heavily creatures, that means you have fewer noncreature cards than normal and potentially less resilience to effects like board sweepers