Not every one-trick will refuse to swap, occasionally some will eventually switch to try and tip the odds even if they’re worse at their non-oneitis.
What I’ve gathered:
Mercy OTPs : Moira. The most terrifying Mercy one tricks are the ones who can only swap to Moira. It usually means “DPS GOD DAMN YOU FUCKING SUCK I’LL DO IT MYSELF WITH EVIL MERCY”. Sometimes Kiriko.
Genji OTPs: Reaper. Usually when their Winston is really good, and they normally do good when they do so. Other than that, Soldier if they still can’t take down their Pharmercy.
Hanzo OTPs: Widowmaker or Ashe. Usually when their Widow is too good or they’re struggling against Pharmercy. Also Reaper if the Winston is really good.
Reinhardt OTPs: DVa when their own DPS can’t play hitscan well. Otherwise Orisa because Rein is really mid outside of gold.
Doomfist OTPs: Yes, this is rare. But usually Roadhog for some reason.
What others? Genuinely cuirious.
Save fade for the hack, fade backwards and the sombra is in front of you.
If they virus instead of hack fade backwards to cleanse and then attack to stop hacks
Also grasp and orb both are easy to use against a sombra trying to flank someone else as you don’t need aim and both interrupt hack.
I might not be able to kill a sombra if they tp and go invisible but once I know there is one on the enemy team it’s very rare they can get the kill on me at least.
I know people suggest kiriko but I have dog shite aim with the kunai
Similar principles with tracer however if tracer has all her blinks and recall fade is unlikely to save you unless you can keep a decent distance and force bullet spread and fall off.