Whenever one or more creatures you control with power 4 or greater attack, search your library for up to that many basic land cards, put them onto the battlefield tapped, then shuffle
It evolves without any hassle (being Stage 1), requires only 2 Energy to attack, and can be summoned quickly via the Find a Friend Eevee (which also helps search for Hydreigon, by the way)
Or this is the third charm
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While other players can stop you drawing from Esper Sentinel, more often than not, they won't want to wait an extra turn to play their spells, more or less ensuring the card at least replaces itself