Beach episode. This one is infamous for its nonsensical plot - even by Sailor Moon standards - and the fact that it's a beach episode.
I'm going to be very real: I don't care about this episode. It's the most filler episode to ever filler, it conttains a surprising amount of shots of the Senshis in their swimsuits (who is this made for?) and it has a weird aquatic creature in it. There is literally no point in watching this episode.