OK, so here's some general notes/advice.
(a) If you're worried about schticks that are taking up actions that would be spent on maneuvers, make them powered by expending maneuvers, and have the effect be dependent on the maneuver level. That way there's auto-scaling, and it's essentially a class feateuver.
(b) It seems like you have a bunch of ideas here. My suggestion is: don't worry about fitting everything into one class and/or tacking on a bunch of ACFs. Figure out what you want the class to be like, and then make a couple prestige classes, feat chains, or ACFs (or even another base class) which explore options.
Part of the problem is you have a glut of ideas for class features, but that's all it is right now -- a collection of cool class features. So, here's what Death Knight means to me: a warrior who commands the power of undeath. Oversimplification? Maybe, but look at everything that
isn't in there.
Brainstormage (feel free to use all or none of this):
~Give what's essentially an undead animal companion from level 1. You could literally have it just be a normal animal companion with one of the undead templates on it. Then, make a 5-to-8-level prc that's enterable at level 3, and requires X ranks in Ride (and maybe Mounted Combat), which turns it into an undead mount. Give access to mounted disciplines there.
~Keep the gradual type change and immunities. It's a time-honored tradition, at least in Magipunk
and it seems really integral to the flavor for me.
~What's the point of knight's command? I think fear-based effects make more sense than drawing aggro. Give immunity-piercing, and then have something like whenever you initiate a maneuver, the target has to make a save vs fear. Let them swap a stance for a frightful presence effect. Alternatively, make this a discipline (or use Stygian Nightmare).
~You have a discipline for short-term animation, cold&neg damage, and energy drain. With the fear effects, that's basically all of a dread necro's fun,
except for the ability to control long-term minions. So for the other real ability, make it so you can choose (via paying some cost) to animate + control someone as you slay them. Makes the class much scarier to go up against: you know that if you fall, the guy will make a mockery of your life by making you serve him past death. They can only control X HD of creatures, which scales up, and also make more powerful minions.