Hellkite Charger triggers, causing you to pay ({5} magic symbol) ({R} magic symbol) ({R} magic symbol) to untap all attacking creatures and to get an additional combat phase after this one.
Deal combat damage using Rith.
Rith triggers, causing you to pay ({2} magic symbol) ({G} magic symbol) to create at least ten 1/1 Saproling creature tokens.
Move to your next combat phase, and declare Rith and Hellkite Charger as attackers.
Hellkite Charger triggers, holding priority, activate Utopia Mycon's second ability seven times by sacrificing seven Saprolings, adding ({5} magic symbol) ({R} magic symbol) ({R} magic symbol) .
Resolve the Hellkite Charger trigger, causing you to pay ({5} magic symbol) ({R} magic symbol) ({R} magic symbol) to untap all attacking creatures and to get an additional combat phase after this one.
Deal combat damage using Rith.
Rith triggers, holding priority, activate Utopia Mycon's second ability three times by sacrificing three Saprolings, adding ({2} magic symbol) ({G} magic symbol) .
Resolve the Rith trigger, causing you to pay ({2} magic symbol) ({G} magic symbol) to create at least ten 1/1 Saproling creature tokens.
Repeat from step 5.
If there are at least eleven permanents of any color on the battlefield, this combo nets infinite Saproling tokens and colored mana.