Popup Dungeon is a turn-based tactical RPG with an added twist being that you can create your own characters, items, abilities, and so on.

The tactical RPG part is reasonable enough - enemies drop items and you might find additional abilities/bonuses on the levels. These stick around for the duration of a chapter, adding a rogue-lite element of sorts.

As for the editor, the game takes basic counter-measures against you creating something absurdly powerful - for example, you can make an ability stronger, but it will need a longer cooldown, higher Action Point cost, limited uses, or negative side effects.

It is, of course, possible to outsmart the game - for instance, your spell might be making its target much stronger after dealing damage, but the enemy will not be able to appreciate this if several spells have been stacked up in such way that this kills them in one hit. I've had my fun with this.

Conveniently, outsmarting the game is precisely what you'll need to do if you intend to play on the higher difficulty levels without grinding the levels for meta-currency to purchase/combine "charms" (5 can be equipped at the time, each offers one or other stat boost for the team).

As for the caveats, we have:

• The charm system is a bit of a headache - bought/reward charms have a random type, and combining charms upgrades them in one or other way (that you'll need to figure out through experimentation or read a guide for).
  
• In my ~30 hours played I could not concretely out whether the game expects you to create your own things to progress.
  Discovering cheesy builds is a common part of this genre, but how cheesy is too cheesy?
  
• The game contains a story mode campaign (split into 25 (?) chapters) and free-play challenges.
  The story mode is interesting (with each new chapter bringing a change of scenery and new enemies, rules, or one-off delights with D20 rolls), but it seems to overstay its welcome a little - personally I quit somewhere around 2/3 of it, and 1.5% of the players have the most recent progression achievement.
  
• The game uses what it calls "game-managed workshop", which means that the only way to browse items is through the in-game UI.
  Personally I have not been substantially impacted as I was making my own designs anyway, but a web-based interface is nice to have for search and comments.