Depending on your difficulty, your Gloom will rarely land a status effect on anything that matters (since Cursed is NOT a mindpower class).
You're intended to switch the sustains, but it depends if you go two hander + shield (Repel and Cleave benefit) or two hander + mindstar (Surge and Cleave benefit). Mindstars make good offhands because of 100% offhand damage, but you sadly can't use the mindstar tree skills besides psiblades with only a single psiblade. Not to mention that they're beastly weapons at T4/5.
Also someone fact check me because I haven't played Cursed in a year or so.
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A little bit of a starters guide written by yours truly
here.