People have brought up that Pathfinder shouldn't technically be damaged by Caustic gas since he doesn't breathe. This got me thinking about other interactions that could create some meta game countering to happen.
Here is a few thing I thought might be interesting:
Bloodhound can't be fooled by Mirage holo's because of his attunement to nature.
Bangalore can't gain her speed boost when being fired at by Octane due to his fast reflexes.
Watson deals extra damage to Pathfinder when he walks through her gates because it short circuits his system.
I am open to more ideas. I love the idea of spicing up the inter-legend interactions and meta in new ways and the more they can interact with each other uniquely the better. Hopefully each legend could have some sort of upperhand against one other legend as to make sure every legend has a weakness.