It doesn't look like Shank is doing anything special.
The most complicated part is probably where one character picks up another character, and that's really easy to do.
Dynamic aiming is easiest done with IK. That's also easy.with Spine PRO.
In that context, I expect you to have no problems using the Spine runtime in Unity.
Spine is just a tool though, and Shank looks like it has some solid technical work (thoughtful decisions on how best to do things without being overly complicated) on top of its skillful animation work.
There may be minor shader work to be done.
A few members here in the forum contributed some shaders. I personally recommend ToddRivers' work: Sprite Shaders for Unity
Though because of some basic cases that Shank handles, I may just post a basic shader myself that covers the same cases.
I also personally recommend that you use the "Spine Native" SkeletonAnimation API rather than the SkeletonAnimator Unity Mecanim API (which is intended for people who really, really like Mecanim and are familiar with Mecanim's quirks).
Also note if you don't want to fully commit immediately, Spine Essential is $69 and you can upgrade to PRO for the difference in price.
I do welcome other users to chime in. You probably shouldn't just listen to one person with nothing to back his claims. :p
