That look a lot like the chicks I've had with slow feathering. So if it's acting healthy, I would just provide heat as long as the chick needs it, but otherwise not treat it any differently than the others.My cornish bamtams had ugly stages too, but nothing quite like this. But the chick is acting just fine and dandy like her siblings. Just way uglier.
But for breeding purposes, remember it can pass on that gene to its offspring, and consider whether you care about that!
Recap of the genetics: slow feathering is on the Z sex chromosome and is dominant. So a female either has it or she doesn't, and a male shows it when he's got one copy of the gene or two. If you have a slow feathering female, and breed to a fast feathering rooster, you get feather-sexable chicks, with the daughters feathering fast and the sons slow but carrying fast.