You have a nonartifact creature card in hand that can be cast using two mana or less.
Steps
Activate Chromatic Orrery's first ability by tapping it, adding ({5} magic symbol) .
Cast a nonartifact creature card from your hand by paying at most ({2} magic symbol) .
When the creature enters the battlefield, Cloudstone Curio triggers, returning Derevi from the battlefield to your hand.
Cast Derevi by paying ({3} magic symbol) .
When Derevi enters the battlefield, it and Cloudstone Curio trigger.
Resolve the Cloudstone Curio trigger, returning the creature cast in step 2 from the battlefield to your hand.
Resolve the Derevi trigger, untapping Cloudstone Curio.
Repeat.
Notes
If the creature can be cast using ({1} magic symbol) or less, this combo nets infinite mana, and you may use Chromatic Orrery's second ability instead, if desired.