Holy shit are you me?? I just did a little side project last week to get my Claude code agents to RP as Abathur with me. Same results for me, it works for the first couple responses, but very quickly regresses to the mean. I tried writing out a prose/voice guide, I didn’t need it to use actual Abathur quotes, but it never seems to stick. I think there’s a thing the caveman mode does that re-injects the instructions to keep it in line, I haven’t gotten around to experimenting with anything yet though.