Not long ago I have not seen this series again, until I found out that it just returned this year ._.

Feels like I haven't seen this series in a while. is it still going?

Really good.
Hope to check out the game when it's ready.

Might consider (for future tests) composing a simple course from basic shapes to drive the parkour theme. It wouldn't just rehearse the tasks of fluid form from obstacles to running to obstacles, but make the test anim's more interesting... just a thought.
On the whole the artwork is great. Motion is fluid and consistent, so picking that apart for your progress would be pointless. I would only like to toss a few thoughts to help (hopefully)...
Their could be some occasions to shift the character from a "squishy" to a "rubbery" or "bouncy" for comic purposes. This being for a game, I'm not entirely sure how to advise incorporating the changes as you build and rebuild (I hope you'd consider at least a couple newer versions and episodes)... You could use a "power up" option or device in the game for consistency, so the player would have to pick when and when not to go rubbery or squishy for future impacts... Or even just a limit on the time of power (like mario-bro's stars)...
Also just for giggles, have you considered breakable items involved in some obstacles, tree branches or certain ledges that crumble, fall apart, or even a wall or two that falls over... etc.
Of course, it's your game and production, so you've likely thought of things like this. I like everything I've seen so far. Keep at it, and I'm sure you'll create a master-work sooner or later. And by all means have fun with it.

These are pretty nice, I'd try to get slightly more impact when he first contacts the wall but what do I know.