Seems that Hydreigon is receiving the love it deserves. Seriously like Gensect, Hydreigon is one of the most diverse Pokemon in or outside of wheather. On sun teams it can fire off(no pun intendted) insanely powerful Fire Blast which roast pretty much any Pokemon weak to and can do heavy damage to Pokemon that are neutral damage to Fire Blast. Hydreigon is also diverse in rain too as it learns Surf and coming off from specs Hydreigon it can 3 OHKO Specially defensive Jirachi in rain and only needs about layers of spikes to 2-3 OHKO Specially Defensive Jirachi in rain.
Calcs
252 SpAtk Choice Specs Hydreigon Surf vs 252 HP/224 SpDef Jirachi (+SpDef) : 41.34% - 48.76%
Entry hazards damage: 67
After entry hazards: 234 - 264 (57.92% - 65.35%)
2-3 hits to KO (with Leftovers)
252 SpAtk Choice Specs Hydreigon Surf vs 252 HP/224 SpDef Jirachi (+SpDef) : 41.34% - 48.76%
3 hits to KO (with Leftovers)
Calcs
252 SpAtk Choice Specs Hydreigon Surf vs 252 HP/224 SpDef Jirachi (+SpDef) : 41.34% - 48.76%
Entry hazards damage: 67
After entry hazards: 234 - 264 (57.92% - 65.35%)
2-3 hits to KO (with Leftovers)
252 SpAtk Choice Specs Hydreigon Surf vs 252 HP/224 SpDef Jirachi (+SpDef) : 41.34% - 48.76%
3 hits to KO (with Leftovers)