Saheeli, the Sun's Brilliance | Mana Echoes | Corridor Monitor

(and one other card)

Saheeli does not have summoning sickness.
({U} magic symbol) ({R} magic symbol) available, plus an additional ({U} magic symbol) ({R} magic symbol) if you control less than three creatures that share a creature type with
Corridor Monitor.

Activate
Saheeli by paying ({U} magic symbol) ({R} magic symbol) and tapping it, creating a token copy of
Corridor Monitor with haste.
When the token
Corridor Monitor enters the battlefield, it and
Mana Echoes trigger.
Resolve the
Corridor Monitor trigger, untapping
Saheeli.
Holding priority, if you control less than four creatures that share a creature type with
Corridor Monitor, repeat steps 1 through 3 one additional time.
Resolve all
Mana Echoes triggers, adding ({C} magic symbol) for each creature you control that shares a creature type with
Corridor Monitor for each trigger resolved this way.
Activate
Urn of Godfire twice by paying ({4} magic symbol) , adding ({U} magic symbol) ({R} magic symbol) .
Repeat.