I've been looking for a simple RPG type game on my phone / ipad for a while and I discovered this one yesterday and have been really enjoying it.
You find / unlock heroes and build them up throughout the campaign and mix and match them to make the best teams for a certain scenario.
It's the sort of game I'm a sucker for where certain things go on cooldowns to entice you to come back multiple times a day, but thankfully this one isn't too heavy on that. It's free to play with optional in app purchases, but from my limited experience so far, they seem completely unneeded as you find and unlock things at quite a quick pace and you get rewards for logging in each day etc.
When you get to level 10 you unluck 'My Dungeon' where you can raid other players / defend your dungeon.
I'm at level 12 now and it looks like there's a whole lot of replayability here and will be a great game for when you're taking a shit.
I'd recommend picking it up and let me know how you find it! I'm still new to it, but if you have any initial questions I'll try to answer them.