For each counter Boon of the Spirit Realm has, every creature you control gets +1/+1
Sevinne, the Chronoclasms Mystic Intellect Flashback deck will help you get your Flashback cards into your graveyard so you can cast them for extra value
And, if general damage isn't your thing but elfball is, pour all that mana into Ezuri, Renegade Leader
So, roll up your maps, hoist your rucksack, and prepare for your journey
Most decks will not be dependant on it, but it will play its role while sitting on the bench and returning discarded supporter cards to your hand
Yannik, Scavenging Sentinel: A legendary creature that can exile another creature you control to distribute its power in +1/+1 counters among other creatures, with the ability to return the exiled card to the battlefield later