Has to be either free or have a free way to get it

There are good games out there, but outside of a few exceptions you can't get a good mobile game for free. If you have netflix, the netflix games selection has some good games, I'd especially recommend Into the Breach. If you have google play pass, there are a lot of good games there was well. As far as truly free good games go, Shattered Pixel Dungeon and Hoplite are the only ones that comes to mind.

If you're willing to spend some money to get something worth your time, I'd recommend Slice & Dice (has a free demo), Reventure, Super Hexagon, VVVVV, Dicey Dungeons, Dead Cells (plays surprisingly well on mobile, play pass includes all DLC), Krumit's Tale, King of Dragon's Pass, and Star Traders Frontiers.