is there a way to unlock dark characters ?

[Fabio92]

I mean the cobra and the three or four that remain. they are bosses during story and arcade mode. I hope you understand who I mean. it's a pity you can't use them

[Sunset Margatroid]

you mean the predators? not exactly although you can play as the bear in the salt mines in the lobby if you menage to get more salt than the other players you also get a dark skin for teh character you are using in the salt mines

[1.2M | Missingno.]

Predators have like, three attacks. They're not built to be playable characters.

[Rocketknightgeek]

You can play as the bear and hunt down the other players if you win in the Salt Mines mode.