If an "Aquaactress" monster you control battles an opponent's monster, during damage calculation: Your battling monster's ATK and DEF each become double its current ATK and DEF during that damage calculation only. If this card is sent from the field to the Graveyard: You can target 1 Aqua-Type monster in your Graveyard; Special Summon it, also you cannot Special Summon monsters for the rest of this turn, except Aqua-Type monsters. You can only control 1 "Aquarium Lighting".
It's not once-per-turn, of course it'll apply for each battle. But the boost isn't permanent, either. Which is what it's saying. Since that's, you know, relevant for direct attacks or cards like Mystik Wok or Riryoku.
Aquactress is a funny and free deck, i think they can be meta with ssa.