Ashaya, Soul of the Wild + Blossoming Tortoise + Spawning Pit + Winding Constrictor + Karn, Silver Golem

Ashaya, Soul of the Wild

Blossoming Tortoise

Spawning Pit

Winding Constrictor

Karn, Silver Golem

How it works

1. Animate Spawning Pit using Karn
2. Activate Spawning Pit's second ability by removing two charge counters from it due to Blossoming Tortoise, creating a 2/2 Spawn artifact creature token.
3. Activate Spawning Pit's first ability by sacrificing the Spawn, putting two charge counters on it.
4. Repeat from step 2.