Tourmaline

The star of the show herself! ... Metaphorically, of course. This place doesn't exactly have 'stars'.
Tourmaline is... not an experienced hunter. She doesn't seem to take any of it seriously, nor does she seem to respect ARTIFACT beyond thinking of them as her friends and family. She seems to always be distracted, checking on other things, wandering around Fantasium while the Moonview Fantasms are meant to stay in their district. And yet, she doesn't. She takes pride in breaking that rule, actually- a Keeper does have to help the other areas, too, after all.
Perhaps her biggest strong suit is that- her tendency to break rules just to help others. An outsider in the Sanctum's main town? Helps find a rather unruly Fantasm claiming to be the Lord of Nightmares and beats him. Also helped find a gateway between worlds. Also helped defeat a rogue robot and its half-machine buddy. There's a lot she's done for the Treebound Sanctum actually... not that she wants to undermine poor Buttercup. She really doesn't. She's just eager to help, is all, and a lot of those problems can't really be solved by entangling the threat in vines for that long after all. She helps with brute force and a little bit of electricity, is that such a bad thing?