Awesome Music: The score might be repetitive, but at least it takes 500 listens to wear on your nerves.
Scrappy Mechanic: The Granny Slug levels implement the theme of sneaking up on Granny while she's napping by sending you all the way back to the beginning of the five-level adventure - yes, even back below levels you've already beaten - if you lose even once, thus "waking her up". It can get extremely frustrating to have to replay the same few levels over and over again just to get one more shot at a level you can't beat, whereas most other levels in the game will only require that you have enough Energy to play again. There have been complaints that these levels are pretty damn difficult, making this a frequent occurrence. Some have even complained that because of how much they had to use to get extra moves over the course of the adventure, the gold that they got upon defeating Granny Slug wasn't nearly worth the trouble.
Initially, the Granny Slug levels didn't even restore the health you used to play each level even if you won, but that was fixed in a later update.
They Copied It, So It Sucks!: The game has received criticism for being too similar to Brave Frontier. Using everything from its cute designs to its level-up system in which characters evolve by reaching certain benchmarks to the basic gameplay scheme, even down to the name which uses the same initials, one could argue it's essentially a more family-friendly version of Brave Frontier.
The similarities extend to how much the first five Fiends resemble the Six Heroes:
Howie = Eze (Both left their homes for a reason and carry something special)
Tantrum = Lance (Both were someone special before going on a big adventure)
Kwincy = Atro and Magress (Kwincy has Atro's superhero tendencies and Magress's loss of their original forms)
Brittle = Selena (Both were the only girls at first)
Ugly Cute: The bugs, especially when they upgrade.
Viewer Gender Confusion: Brittle's younger forms, Snap and all of Karma's forms are easily mistakable for male, as they lack eyelashes and lipstick like other female Fiends. You may have to read their descriptions to get details like these, though even then that's not always reliable as their descriptions may change between updates (for example, Karma's description no longer specifies her gender). In the November 2020 update, Alien Brittle is said to be a male (, even though Brittle is a female, though this is only in-game, as her website bio keeps her with feminine pronouns.