Steelswarm Operator + Agatha's Soul Cauldron + Horseshoe Crab

Steelswarm Operator

Agatha's Soul Cauldron

Horseshoe Crab

How it works

1. Activate Steelswarm Operator's second ability by tapping it, adding that can only be spent to activate abilities of artifacts.
2. Activate Steelswarm Operator using Horseshoe Crab's ability by paying , untapping it.
3. Repeat.

This clever loop turns Steelswarm Operator into a self-sustaining mana engine by leveraging Agatha's Soul Cauldron. Because Agatha's Soul Cauldron grants creatures with +1/+1 counters the activated abilities of exiled creatures, you can exile Horseshoe Crab to put a counter on Steelswarm Operator, giving the artifact creature the Crab's untap ability. From there, you tap Steelswarm Operator for its restrictive blue mana—using a portion of it to pay the Horseshoe Crab ability cost—allowing you to untap the Operator and repeat the process for an infinite supply of blue mana dedicated entirely to artifacts.