Saheeli, the Sun's Brilliance | Mana Echoes | Great Oak Guardian

(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
Great Oak Guardian.

Activate
Saheeli by paying ({U} magic symbol) ({R} magic symbol) and tapping it, creating a token copy of
Great Oak Guardian with haste.
When the token
Great Oak Guardian enters the battlefield, it and
Mana Echoes trigger.
Resolve the
Great Oak Guardian trigger, untapping all creatures you control and giving them +2/+2 until end of turn.
Holding priority, if you control less than four creatures that share a creature type with
Great Oak Guardian, 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
Great Oak Guardian for each trigger resolved this way.
Activate
Gemstone Array's first ability twice by paying ({4} magic symbol) , putting two charge counters on it.
Activate
Gemstone Array's second ability twice by removing two charge counters from it, adding ({U} magic symbol) ({R} magic symbol) .
Repeat.