Mechtitan Core | Prototype Portal | Myr Battlesphere

(and two other cards)

Mechtitan Core in exile (exiled by
Prototype Portal).
All other permanents on the battlefield.
You control at least three other nontoken artifact creatures and/or nontoken Vehicles.
({7} magic symbol) available.

Activate
Prototype Portal by paying ({2} magic symbol) and tapping it, creating a token copy of
Mechtitan Core.
Activate the
Mechtitan Core token by paying ({5} magic symbol) and exiling it,
Myr Battlesphere, and any three other nontoken artifact creatures and/or nontoken Vehicles, creating a 10/10 Mechtitan creature token.
Activate
Ashnod's Altar by sacrificing the Mechtitan token, adding ({C} magic symbol) ({C} magic symbol) .
The Mechtitan token dies, triggering
Dross Scorpion and
Mechtitan Core.
Resolve the
Dross Scorpion trigger, untapping
Prototype Portal.
Resolve the
Mechtitan Core token trigger, returning all other cards exiled by it to the battlefield tapped.
Myr Battlesphere enters the battlefield, creating four 1/1 Myr artifact creature tokens.
Activate
Ashnod's Altar three times by sacrificing three Myr tokens, adding ({C} magic symbol) ({C} magic symbol) ({C} magic symbol) ({C} magic symbol) ({C} magic symbol) ({C} magic symbol) .
Dross Scorpion triggers three times, allowing you to untap up to three artifacts you control.
Repeat.