Requires

Morselhoarder must be on the battlefield. Sinking Feeling must be on the battlefield. Multani's Harmony must be on the battlefield. Mana needed:

Steps

1. Activate Morselhoarder by tapping it to add a mana of any color.
2. Activate Sinking Feeling, by paying and putting a -1/-1 counter on Morselhoarder to untap it.
3. Activate Morselhoarder by removing a -1/-1 counter from it to add a mana of any color.
4. Repeat.

Results