One of the best - if not the best - casual games i've played.
The concept is very simple, it's like an old Snake game.
But in this case, instead of snake sections, each part is an RPG inspired unique character, with their own upgrade option, increasing abilities and providing you to progress through the apparentely endless difficulty increase in the same bunch of scenarios.
You grind to upgarde the 16 different characters - the maximum of your party - by playing with them and collecting gems while playing to purchase them.
You cannot touch your own party - you kill them. You have to avoid different enemies on each scenario, each one with their own abilities and also avoid contact to don't get killed. You collect coins which you can use to purchase essential power-ups on hard levels or even skip scenarios, as well as hire party members for the next level.
Although the game have it's own currency, it have not something like micro payments or any indications of it. It's a pure grindy game as it is.
Funny, addictive, awesome time killer.
Or when you just wanted to recline the chair playing some funny arrow-based casual game.
Absolutely recommended, except it's not your genre.