Lullmage Mentor + Primal Vigor + Mondrak, Glory Dominus + Elspeth, Storm Slayer

Lullmage Mentor

Primal Vigor

Mondrak, Glory Dominus

Elspeth, Storm Slayer

How it works

1. Whenever an opponent casts a spell, activate Lullmage Mentor by tapping seven untapped Merfolk, countering that spell.
2. Lullmage Mentor triggers, creating a total of eight 1/1 Merfolk creature tokens.
3. Repeat.

This magnificent loop begins when you tap seven untapped Merfolk to activate Lullmage Mentor's ability, countering an opponent's spell. That successful counter triggers Lullmage Mentor to spawn a Merfolk token, but because replacement effects from Primal Vigor, Mondrak, Glory Dominus, and Elspeth, Storm Slayer all double the token generation simultaneously, that single trigger yields an explosive eight new Merfolk at once. With seven of those fresh recruits immediately available to tap along with Lullmage Mentor itself, you have precisely the quorum needed to counter the next spell and repeat the cycle indefinitely.