Like, games that you have played through multiple times, but you still like to replay them from time to time because you can just relax and have a good time without too much hassle.
For me some are Dark Souls 1&2 and Borderlands 1, I can play them without too much thoughts about what I’m doing, but still be focused enough so no bad thoughts appear.
Mega man 2. It was my first Mega Man fame back in the day and I played the shit out of it. So I just play it every so often and it is just so comfortable for me.
Honorable mentions: soul blazer on SNES, the first few levels of the original DOOM, the first TMNT game on Gameboy, it is terrible but just so mindless and short.