Once per turn: You can target 1 monster your opponent controls; change its ATK to 0 until the end of this turn. You must control a Beast-Type monster (other than this card) to activate and to resolve this effect.
After you Fusion Summon Koalo-Koala using Sea Koala as 1 of the materials, you can Special Summon Sea Koala to the Field using Powerful Rebirth, and since you control Koalo-Koala, you can use Sea Koala’s effect to make 1 of your opponent’s monster’s ATK to 0.
You can send this card to the Graveyard; Special Summon 2 Level 3 or lower Beast-Type monsters from your Deck, but they have their effects negated, also they are destroyed during the End Phase. You can only use this effect of "Rescue Cat" once per turn.