Hi, I'm going to browse through and see what I spot. Can't guarantee I see the full picture, but I hope that we can get talking about things and then go deeper as needed. I'm writing this as I go, so things might make more sense later on... we'll see how I edit this.

1) hitdice: 2d4 - an odd choice, but an interesting one. I assume this doesn't just mean a different way to calculate your HP at level up, but also more HD in the short rest category (and probably features I'll be reading about shortly)

2) Multiclassing. While you mention what stats you need to multiclass, you don't mention what skills/etc you gain when you take your first multiclassed level of skinchanger.

3) "your mantle can't be forcibly taken from you" <== does this mean it's literally attached to you? How about damage? (This is a risk with building a class with an item as basis. Maybe go the Warlock route where you can recreate the item? Or even just assume the item is an idea and not a physical one for most of it?)

4) Is the speak with animals part also limited to animals associated with your mantle?

5) Blood scent: Interesting (feels similar to certain sharks I think?) However, in a more "lived in" universe... how often won't there be a random hurt bird, insect or other critter in that radius? The usefulness of this ability will be very much based on how realistically the DM will handle it. After finding 7 dead rats, your player will stop using it. But if you find that hurt enemy 1 mile away... what kind of nature is naturing around there?

6) Primal rage seems... powerful at low levels. Both the extra attack and the regeneration. Granted, the regeneration might be weaker than resistance to physical damage... in certain situations, but the extra attack will often overpower the rage damage bonus (comparing to barbarian). So yeah... not sure about the balance on this one.

7) keen senses: the first part seems okay, basically a non scaling proficiency bonus to perception (due to being a different bonus, it might go insane if you do take perceptive, expertise and other fun things). The second part though. That's quite the powerful ability. (Though technically this doesn't affect hiding/stealth, but probably intended to affect it none-the-less). This pretty much says nope to rogues and most other forms of ambush. Which seems over the top to me.

8) Lesser skin change. The 10 minute to transform and then 1 hour duration seems harsh... maybe make it 1 minute (enough to make it non combat viable/roleplay interesting, but not quite so long). Beyond that, the temporary hitpoints/transforming back isn't described properly. I assume it works like a druid "new shape HP, and if you drop below zero, you take the rest of the damage in your normal form"? I'll probably be back to this feature once I get to the mantle part of the document.

9) ASI: the text says normal (4,8,12,16,19) while the table has fighter style (4,6,8,12,14,16,19) - which is it and why? (and if you go normal, maybe move one of the level 7 abilities to level 6, etc)

10) The 10 to 17 range of levels are interesting, but a bit heavily stacked. Not quite sure yet and not going to look to deep into it at this point in time.

11) At level 18 you are basically immortal, aren't you? To everything except time... though technically even that isn't true from what's written.

12) the powerful build is good, the added two handed weapons... might be a bit much (and the heavy property won't even count for most characters)

13) wild summons... I'd do this more like a normal summon spell. So lowest amount of creatures and lowest CR at level 3. Either more creatures or higher CR at level 5, etc. As 6+prof boars at level 3... is going to seriously add some muscle to a party.

Anyhow, long story short, my conclusions:
  • I like the idea and feel alot.
  • There's a bit too much going on for this class at many levels (lots of "good ideas" + "extra bonus for me" feeling)
  • And finally, the combination of rage+shapeshift+summon might just be a bit too much at the same time.