I've been farming Duke Fishron because I'm playing ranged and I need his bow to progress further in the game. The thing is, I've defeated him over 40 times and I got 0 Tsunamis. 0. I got all other items, including ones with a lower chance of coming compared to Tsunami's (wings came multiple times, 6.67% ; Tsunami = 20%). Chances of me losing 40 times >>in a row<< are 0.0001% and as I'm writing this it's getting even lower because I have not acquired my item. All other ones, the trophy, the mask, the wings: I've got them all, except my bow.