Spirit of the Season is a uncommon Creature — Treefolk Spirit card from Unsanctioned (UND), collector number 70. Current market price: $0.21, TCGplayer market prices via Scryfall.
When this creature enters, it gains haste if it's summer. Put a +1/+1 counter on it if it's autumn. You gain 5 life if it's winter. If it's spring, search your library for a basic land card, reveal it, put it into your hand, then shuffle.