Berta, Wise Extrapolator + Agatha's Soul Cauldron + Farmstead Gleaner + Clockwork Hydra

Berta, Wise Extrapolator

Agatha's Soul Cauldron

Farmstead Gleaner

Clockwork Hydra

How it works

1. Activate Berta using Clockwork Hydra's ability by tapping them, putting a +1/+1 counter on Berta.
2. Berta's second ability triggers, adding one mana of any color.
3. Activate Berta using Farmstead Gleaner's ability by paying 2 and untapping them, putting a +1/+1 counter on Berta.
4. Berta's second ability triggers, adding one mana of any color.
5. Repeat.