Agatha's Soul Cauldron + Wildwood Mentor + Phyrexian Altar + Thopter Squadron

Agatha's Soul Cauldron

Wildwood Mentor

Phyrexian Altar

Thopter Squadron

How it works

1. Activate Wildwood Mentor using Thopter Squadron's first ability by paying 1 and removing a +1/+1 counter from it, creating a 1/1 Thopter artifact creature token.
2. When the Thopter enters the battlefield, Wildwood Mentor's first ability triggers, putting a +1/+1 counter on itself.
3. Activate Phyrexian Altar by sacrificing the Thopter, adding 1.
4. Repeat.