Hoping that Yowashi (Yo, it's your boy Washi) has some interesting mechanic behind it regarding its form change.
Something I'm thinking about (and will probably not happen) is that you catch the singular Yowashi in the wild, but once you catch more and more, you have the ability to 'stack' them and create a school of Yowashi that count as an individual 'Mon. Single Yowashi would have high speed, but be pretty frail. School Yowashi would have low(er) speed - I'd imagine it's harder to co-ordinate and navigate an entire school - but higher defence stats.
I could also see School Yowashi being the Water Totem. It could summon Single Yowashi. Then perhaps it'd have a move / ability where it's able to subsume the Single Yowashi into its School. Perhaps that could give it a stat boost (I was initially thinking a +1 in defence, but maybe a random +1 instead?), or even a HP restore (adding the Single Yowashi's remaining HP to the School's remaining HP, up to max [i.e School Yowashi has 80/100 HP, Single Yowashi has 16/16 HP. School Yowashi subsumes, get 16 HP restored to 96/100 HP.])?
Basically, lots of cool stuff could happen with this mon. It probably won't. I quite like it's design regardless, the Single Yowashi moreso than the School Yowashi. It's cute and helpless.