Rock Hydra [Foreign Black Border] HGSS01 Set: Theros Beyond Death Type:

Set: Theros Beyond Death Type: Creature — Merfolk Wizard Rarity: Rare Cost: {U}{U} When Thassa's Oracle enters the battlefield

They only specify the consequences should you fail

Sometimes quantity

Set: Rivals of Ixalan Promos Type: Creature — Merfolk Shaman Rarity: Rare Cost: {3}{G} Whenever World Shaper attacks

It gains +1000 power during this turn

Rock Hydra [Foreign Black Border] HGSS01 Set: Theros Beyond Death Type:Set: Foreign Black Border Type: Creature Hydra Rarity: Rare Cost: {X}{R}{R} Rock Hydra enters the battlefield with X +1 +1 counters on it. For each 1 damage that would be dealt to Rock Hydra, if it has a +1 +1 counter on it, remove a +1 +1 counter from it and prevent that 1 damage. {R}: Prevent the next 1 damage that would be dealt to Rock Hydra this turn. {R}{R}{R}: Put a +1 +1 counter on Rock Hydra. Activate only during your upkeep.