I don’t think I’ve seen a tree puppeteer-ing a suit of armour before – it’s a cool idea

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It is a moving tree, how does it otherwise impersonate a guy wearing armour. All in all, it is sentient, and moves.
They’re saying - does it walk about, or it is fixed and just waves limbs?
I assumed a fully walking tree in a sort of mangrove style like a spider ‘cos it seemed more fun (if you preferred the big gnarly roots you could look at English Oak and Chestnut).
The comments about construction are probably aimed at some of the wobbly shapes and proportions; branches don’t seem to taper and idk what the spiky bits are. For the canopy I’d say less ‘blobby’ and more of a major mass with some ‘children’ for variety. Form-wise try lighting basic geometric stuff before texturing; the stamping patterns you've used I kinda like, but make sure they wrap around the underlying shapes. You seem to doing a bunch of this stuff in the pencil sketch already so apply it!
I didn’t get around to the armour, but it looks a bit invented: find a nice reference for proportions and materials first, and you can stylise however you want. atm your shading just doesn't look very confident; it’s hugging the edges a bit. I’d lose the legs of the latest ver. and probably the gauntlets too; you could maybe have the roots popping out to hold stuff.