Activate Marvin using Cryptic Trilobite's second ability by paying ({1} magic symbol) and tapping it, putting a +1/+1 counter on Marvin.
Activate Marvin 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.
Activate Marvin using Farmstead Gleaner's ability by paying ({2} magic symbol) and untapping Marvin, putting a +1/+1 counter on Marvin.
Activate Marvin 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.
Notes
Once you have infinite ({C} magic symbol) that can only be spent to activate abilities, you may forego removing the +1/+1 counters from Marvin.
Results
Infinite colorless mana that can only be spent to activate abilities.