Mikaeus and Night of Souls' Betrayal on the battlefield.
Steps
Cast Cryptic Trilobite for X = 0 by paying ({0} magic symbol) .
Cryptic Trilobite dies due to having zero toughness.
Cryptic Trilobite's undying ability from Mikaeus triggers, returning it to the battlefield with a +1/+1 counter.
Activate Cryptic Trilobite by removing the +1/+1 counter from it, adding ({C} magic symbol) ({C} magic symbol) that can only be spent on activated abilities.
Repeat from step 2.
Results
Infinite colorless mana that can only be spent on activated abilities.