So I finished up the Cell rig (after completely re-doing it a few times to get it right) using a cross between skin wraps and manual skinning:

However, when i went to import it into BrawlBox to test it, this popped up:

How can I fix this?

I'll do my best

Well I think the rig's looking pretty good for the most part, although these hands are completely messed up in BrawlBox.

and of course, I have to figure out how to optimize it without losing the rig. I read through the tutorial here on the forums, but my version of 3ds max doesn't let me move the skin or pro optimizer, so i can't drag the skin to the top.

That definitely would come in handy.

EDIT: Actually, I forgot to do the mouth and teeth. Any tips/things to consider while doing so?

So here's the final rig:

It's actually Facepoint count that matters, not the Poly count. Though unfortunately, you can only check the Facepoint count after importing into BrawlBox.

The absolute maximum Facepoint count is about 17k Facepoints, and even then, there's a chance there may be slight lag.

hmm....Okay, I shall see what I can do. Thanks KJP

Also, did an arm:

update on Cell rigging:

I ended up redoing him completely, and now i'd say he's looking rather good. The poly count is really high again, though i did optimize it. Problem is, I'm not sure if moving the optimization back to the top will keep the rig intact.
The tricky part here was getting the knee to look the way I wanted it to, seeing as Cell's body isn't stretchy like human skin. The green/dark navy armor should be hard and rigid. There'll be some clipping in-game due to this, but i still think it'll be accurate to what Cell would actually be like.

In the Edit Mesh Modifier, click on Polygon, then scroll through the tools and click on "Create", then click on each of the vertices around the hole to fill in that game. Texture may or may not be properly mapped, 3ds Max is a little finicky with that.

And it worked like a charm! Thanks.

One thing I would like to know is how to patch up holes, like this one for example:

Please excuse my ignorance lol

I decided to start with something simpler first, so I'll put this here Cell on Captain Falcon because why not

Rig it as you normally would the regular hair. It's not so much as what you rig it to but what the visibility bone is. In this case many for a certain expression or the common finals smash eyes visibility.

Ok, so then what do I need to do in order for his regular hair to not show up once the visibility bone is active?

Yeah, the textures on them all right now are just what came with the models lol and @Gamidame_K: no big deal, I don't see myslef doing all of them anyway

I think i'll most likely try to retexture them. I also need some rigging help/pointers for this guy here:

 I just got Maya after posting those other previews, and although the concept is easy, it's knowing what to rig that I need some assistance on. The trunks PSA over Ike (and many other PSAs) have it where certain parts of the model only appear when activated (ssj transformations in this case) I'm not sure what to rig the ssj hair to.

Well I got my hands on a bunch of Xenoverse models They're all pretty high poly of course, but i'm sure at least parts of them could be of use.

I have a loooot more than just these also.
 I'd like to try my hand at a couple of them, but with my limited rigging ability I think it'll be best to share the models with whomever wants to use them for a hack. I would put the vegeta/goku/kid buu models i have with the PSAs, but i  have no idea how to deal with all the model changers and stuff like that. If anybody wants to use them, just pm me and i'll send them to you in either a 3ds max scene or just as .obj's! All credit for them would be to Postmortacum on DeviantArt and forfun08 on facepunch. I just used a program to convert them to obj.

Is that so? Ok, so that ended quickly. No big deal.

Well that's good to hear. Guess I'll be doing a Link version and N.Zero PSA version

Has anyone done this yet?