Farmstead Gleaner and Empowered Autogenerator in exile (exiled by Myr Welder).
Myr Welder does not have summoning sickness.
({1} magic symbol) available.
Steps
Activate Myr Welder using Empowered Autogenerator's ability by tapping it, putting a charge counter on Myr Welder and adding one mana of any color for each charge counter on Myr Welder.
Activate Myr Welder using Farmstead Gleaner's ability by paying ({2} magic symbol) and untapping it, putting a +1/+1 counter on Myr Welder.