Cryptic Trilobite has at least one +1/+1 counter on it.
({3} magic symbol) ({U} magic symbol) available.
Steps
Activate Viral Drake by paying ({3} magic symbol) ({U} magic symbol) , putting a +1/+1 counter on Cryptic Trilobite.
Venser triggers, creating a legendary 3/3 The Hollow Sentinel artifact creature token.
Activate 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 Relic of Legends' second ability by tapping The Hollow Sentinel, adding ({U} magic symbol) .
Activate Ashnod's Altar by sacrificing The Hollow Sentinel, adding ({C} magic symbol) ({C} magic symbol) .