I have the video korean player clear the hell difficulty with only 3 star-character's. It was blood battle which it took 27 minute to win. https://www.youtube.com/watch?v=675XMwLFEpU
There are maps you can enjoy uneven battle field like height against moving restriction and fence for defense. Sometimes you need to pierce the enemies to escape the cliff etc.
Just grabbed this and the base game is really well done with lots of stuff to do. However it seems more of a "freemium" game after it has gone free. It has stamina and a bunch of different currency to confuse me with. Hard to say if I'll keep going because of all that. For the dev: I think this game would look a lot better with a new loading screen since the current one makes the presentation look bad (swirly background and old school loading bar). Also the icon could use a better quality image. It looks like a low quality jpeg image :/ Lastly I can generally understand the English but I think this game would be a lot more popular if you got someone to fix the English for you!