Already done, am doing and will keep using. May I introduce Nylf Schwarz Draconis I and Rito, the Flygon/Rayquaza and Tropius belonging to Drake Dragonheart of Emerald Lands. Nylf is literally petrified/traumitised by ice. He 'freezes' up when he sees ice attcks, no pun intended. And Rito is afraid of the water. Not water attacks, but bodies of water, like pools, the sea and lakes whatever. Even ponds make him nervous. So, in an amazing twist, when Drake fights a water specific trainer, he can't use his best pokemon Nylf, for risk of ice attacks, and Rito who would have a huge advantage as it's at the league on the water field. And did I mention his opponent's his...NO SPOILERS!
Now EC would want justification. Nylf's Drake's starter, and when Drake was about ten, Team Aqua tried to enter Regirock's tomb, and Nylf's 'mom' was the guardian of Regirock's tomb, so she tried to stop them. Team Aqua sent out two Glalies, froze her in a block of ice, and then dumped her in the sea, where she eventually died of hypothermia. Nylf saw them do the deed of freezing her, then saw her dead body on the news. Therefore he is traumitised. And yes Nylf's shiny before you ask. So it's sue-ish that I have a traumitised Shiny as a starter. Nylf ain't no sue.
And Rito was flying along, when something attacked him and one of his wings/leaves was broken, and he fell into the river below, and being a Tropius he couldn't swim, and so he would have drowned if Drake hadn't been fishing nearby, and caught the Tropius. Drake then raised him back to health and caught the Tropius. And no this Tropius ain't shiny.