Empowered Autogenerator and Gilder Bairn in exile (Empowered Autogenerator and Gilder Bairn exiled by Myr Welder).
Myr Welder and Encroaching Mycosynth on the battlefield.
Myr Welder does not have summoning sickness.
({1} magic symbol) (at most) available.
Steps
Activate Myr Welder using Empowered Autogenerator's ability by tapping it, putting a charge counter on Myr Welder and adding ({G} magic symbol) or ({U} magic symbol) for each charge counter on Myr Welder.
Activate Myr Welder using Gilder Bairn's ability by paying ({2} magic symbol) ({GU} magic symbol) and untapping it, targeting any permanent.