The Gitrog Monster [Shadows over Innistrad] Giant Warrior put a +1/+1 counter on

put a +1/+1 counter on Jackknight

Others aren't so obvious

sacrifice any number of creatures

Set: Guilds of Ravnica Type: Instant Rarity: Rare Cost: {1}{B} Undergrowth — Search your library for a black card with converted mana cost less than or equal to the number of creature cards in your graveyard

The Gitrog Monster [Shadows over Innistrad] Giant Warrior put a +1/+1 counter onSet: Shadows over Innistrad Type: Legendary Creature Frog Horror Rarity: Mythic Cost: {3}{B}{G} Deathtouch At the beginning of your upkeep, sacrifice The Gitrog Monster unless you sacrifice a land. You may play an additional land on each of your turns. Whenever one or more land cards are put into your graveyard from anywhere, draw a card.