The Horus Heresy [Universes Beyond: Warhammer 40,000] Sponge Isleback Spawn gets +4/+8 as

Isleback Spawn gets +4/+8 as long as a library has twenty or fewer cards in it

When Vengeful Ancestor enters the battlefield or attacks

Set: Ikoria: Lair of Behemoths Type: Creature — Beast Rarity: Uncommon Cost: {1}{G}{U} Mutate {3}{G/U}{G/U} (If you cast this spell for its mutate cost

" —Foot soldier

Set: Coldsnap Type: Enchantment Rarity: Rare Cost: {1}{R} Cumulative upkeep—Add {R}

The Horus Heresy [Universes Beyond: Warhammer 40,000] Sponge Isleback Spawn gets +4/+8 asSet: Universes Beyond: Warhammer 40,000 Type: Enchantment Saga Rarity: Rare Cost: {3}{U}{B}{R} (As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.) I For each opponent, gain control of up to one target nonlegendary creature that player controls for as long as The Horus Heresy remains on the battlefield. II Draw a card for each creature you control but don't own. III Starting with you, each player choses a creature.