Puzzle and Dragons.
The age-old classic. Mindless match three gameplay with a very, very fragile RPG/Stats/Gacha layer on top.
Battery drain, hardware/software requirements and bandwidth usage are pretty much nonexistent after the initial install, and an intermittent and slow connection is good enough. The baiting for the premium currency is somewhat subdued, and it's good fun even without spending real life monies.
This is how these kind of games should be.
Also, currently fighting vanilla FTL. Dear god, I had so many mods and such installed the last time I played this on PC, it's practically a new game experience again. Getting really, and I mean, REALLY tired of the OST though, despite it being excellent.
Last but not least, just got fed up with Deck de Dungeon again. I have a love/hate relationship with these games. Card/Deck-based dungeon crawling is serious fun, but the localisation is turrible and the flaws are eating into my motivation.
Then, three months later, I discover the icon somewhere and am sucked back in. Sigh.