I dont think Oberyn did. Some people believe that since he uses poison on his spear. But he has never once poisoned someone like a ninjaYeah and some other people say Oberyn Martell may have poisoned Tywin but none of the "Tywin was dying" theories make any sense.
Fuck u
That's not his style. Oberyn wanted Gregor to out tywin. Then he wanted to cut tywins head off in single combat
You say there's no evidence, but I doubt you know about the tyrell money found underneath a certain jailers chamber pot
That jailer was one of varys's secret identities (the one he used to speak to ned stark for example). Varys had to leave real quick due to what tyrion did, so he left evidence like that behind
There's also the stench during tywins vigil. Yes he was killed while pooping, which was a nice nod to "in the end, tywin lannister did not shit gold"
but he was cleaned up by maesters before his vigil. Yet his stench was extra ordinary as if he had been dying of poison.
Olenna specifically mocked his stench at the vigil
Olenna had effectively killed him before tyrion did. Stop being sexist