Goblin Welder + Corridor Monitor + Dross Scorpion + Liquimetal Coating

Goblin Welder

Corridor Monitor

Dross Scorpion

Liquimetal Coating

How it works

1. Activate Liquimetal Coating by tapping it, causing Goblin Welder to become an artifact in addition to its other types until end of turn.
2. Activate Goblin Welder by tapping it, sacrificing Dross Scorpion and returning Corridor Monitor from your graveyard to the battlefield.
3. Dross Scorpion and Corridor Monitor trigger.
4. Resolve the Dross Scorpion trigger, untapping Goblin Welder.
5. Holding priority, activate Goblin Welder by tapping it, sacrificing Corridor Monitor and returning Dross Scorpion from your graveyard to the battlefield.
6. Resolve the Corridor Monitor trigger from step 2, untapping Goblin Welder.
7. Repeat from step 2.