During a Summon Pool Event, you can summon from a unique pool of Champions. Each Event will have its own unique pool of Champions that can be summoned. Champions of the same Rarity have an equal chance of being summoned.
Prism Crystals are required to summon Champions from the Prism Shard.
When a Summon Pool Event ends, any remaining Prism Crystals will be used automatically and summoned Champions will be sent to your Inbox. If you do not have enough Prism Crystals to summon a Champion at the end of an Event, you will be able to use these remaining Prism Crystals in future Summon Pool Events.