Requires

Mechtitan Core must be in exile (exiled by Prototype Portal). Prototype Portal must be on the battlefield. Myr Battlesphere must be on the battlefield. Dross Scorpion must be on the battlefield. Krark-Clan Ironworks must be on the battlefield. Mana needed:

Steps

1. Activate Prototype Portal by paying and tapping it, creating a token copy of Mechtitan Core.
2. Activate the Mechtitan Core token by paying and exiling it, Myr Battlesphere, and any three other nontoken artifact creatures and/or nontoken Vehicles, creating a 10/10 Mechtitan creature token.
3. Activate Krark-Clan Ironworks by sacrificing the Mechtitan token, adding .
4. The Mechtitan token dies, triggering Dross Scorpion and Mechtitan Core.
5. Resolve the Dross Scorpion trigger, untapping Prototype Portal.
6. Resolve the Mechtitan Core token trigger, returning all other cards exiled by it to the battlefield tapped.
7. Myr Battlesphere enters the battlefield, creating four 1/1 Myr artifact creature tokens.
8. Activate Krark-Clan Ironworks three times by sacrificing three Myr tokens, adding .
9. Dross Scorpion triggers three times, allowing you to untap up to three artifacts you control.
10. Repeat.

Results