Since you said criticism is fine, hopefully the mods won't jump on me.
Your color choice is... not great, to put it lightly. I know OJ and Erk don't have the best shading, but the colors lack contrast. I physically couldn't tell there was a lighter shade on Erk's hair until I put my face basically against the screen. I'd recommend using something like Carlyle's cloak from FE8 as an example of darker colors. Speaking of, while it doesn't seem like it's technically darker than the outline, it's still way too close for comfort. OJ's on the other hand is... is that even the same color ramp as the base sprite? I can't tell. Looks off either way.
Mage!OJ has saturated to hell blues and greens. You only have to look at BladeHero's stuff to see why that doesn't look great. You can keep it being dark blue (though, I'd recommend against using both dark green and dark blue at the same time, it doesn't look great in general. A dark blue and a brown or dark orange would probably work better), but use softer colors like on Colm, Hector, or Ephraim.
Erk's anatomy... just doesn't make sense, ngl. Erk's head is tiny in comparison to his broad shoulders. It's like a goomba from the Super Mario Bros. movie. Narrow the shoulders in more, and possibly make him not as tall to not give him the goomba look.