Activate Mairsil using Endling's third ability by paying ({B} magic symbol) , giving Mairsil undying until end of turn.
Activate Mairsil using Blood Vassal's ability by sacrificing it, adding ({B} magic symbol) ({B} magic symbol) .
Mairsil dies, triggering its undying ability, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
Activate Mairsil using Cryptic Trilobite's first ability by removing a +1/+1 counter from it, adding ({C} magic symbol) ({C} magic symbol) that can only be spent to activate abilities.
Repeat.
Results
Infinite black mana.
Infinite colorless mana that can only be spent to activate abilities.