Every generation has introduced at least one real fucking cool fish. From generation 3 came probably the highest quantity of awesome fish (whiscash, relicanth, milotic, etc.), but generation 9 has produced the two best fish of the whole series: dondozo and tatsugiri!
The concept, design, and execution are phenomenal. This is what pokemon was always meant to be. Don’t sleep on the fishes unless you want to be sleeping with the fishes!