Medomai the Ageless, Preeminent Captain, Maskwood Nexus, and Crystal Shard

Prerequisites

• Medomai the Ageless in hand
• Preeminent Captain on the battlefield
• Maskwood Nexus on the battlefield
• Crystal Shard on the battlefield
• Preeminent Captain does not have summoning sickness
• or The opponent(s) being attacked can not block and kill Preeminent Captain
• The opponent(s) being attacked can not block Medomai
• each turn available

Steps

1. Attack with Preeminent Captain, putting Medomai onto the battlefield tapped and attacking
2. Medomai triggers on combat damage, granting you an extra turn
3. Tap Crystal Shard, returning Medomai to your hand
4. Repeat

Results

• Infinite turns