Reasons!:  
Hydriegon stats:  
HP:92  
Attack:105  
Defense:90  
Special defense:90  
Special Attack:125  
Speed:98
 
All adding up to 600  
Douartet stats:  
HP:108  
Attack:198  
Defense:190  
Special defense: 180  
Special Attack:54  
Speed:98  
All adding up to 828 respectively
 
Douartet’s ability: Dark Ambassador;The user is shown as a being of dominance against common odds, making them immune to fighting, bug, and fairy. Sound types have a hard time hitting the target.
 
Move pool:  
Tornado Crunch;The user throws itself at the opponent and chomps at it like a deadly tornado 2-5 times. May cause flinching.  
Pow:30  
Acc:90  
PP:15  
Dragon Dance  
Foul Play  
Icicle Crash