I have tomb king skellies units and I want to have rust on their gleaming metal blades. Any tips?

I would try drybrushing lightly a rust color

Cover the metallic area liberally in Flesh Wash or Brown Ink, and then lightly clean it with kitchen towel/the foam you get in the back of blister packs/your thumb. This leaves reddish-brown stains in the recesses, and dulls the shine of the metallic paint on the flat surfaces, but takes a bit of practice - you don't want to waste ink by painting it on and scraping it all back off.

or use mine, colour it black, wait for it to dry, use a kind of really dark brown and just with the slight cotton bud, rub some bits off it, and you should get rust.

yours sean