Ninja: Walk in shadow.

[Rex]

Didn't Yoshi-P at E3 announce that Ninja would be focusing on DEX as their primary stat? Because I remember people saying "but DEX is ranged..."

Also, hand signs are pretty quick...I assume they can be done on the go...so maybe fights with a lot of movement won't be an issue like you point out at the end of your OP.

Lastly, we definitely know Ninja will have a poison ability since in the video there's a "poison" animation, and Yoshi-P said at E3 that there's an ability that puts poison on your blades. I think that's pretty cool. Then everything you hit gets poisoned.