all bloomburrow cards mtg Booster Pack Play : (BLB) : Toys & Games 4 cards of rarity Rare or higher and 3 20x Bloomburrow 4 Seasons Full

That said, Leviathan is one of the returning Summons of the series, often one of the primary ones, since it is attached to water

LordBlackblade says

Rather, a second "reflexive" ability triggers when you remove a counter from Slumbering Walker this way

The idea was that the tokens would have underscores where the name would normally be, letting you write in your character name

Getting the trigger multiple times on each end step is tricky, but doable if you leverage politics alongside cards like Hunted Horror, or simply muck things up with cards like Bloodchief Ascension and Vile Consumption that burn your opponents on their turn