[Transient Fortitude] can be swapped out for [Blind Rage] if you don't feel you need the efficiency or [Overextended] if you wanna go for a more range oriented build.
I recommend max range Shadow build with Umbral mods and [Continuity], this allows you to switch to shadow pull in an entire room then switch back to Sevagoth use 2nd ability to prime the pile of enemies then nuke with ur 1st ability.
Condemn feels alot more effortless to use then Gloom with my [Sevagoth] playstyle as i tend to power up Shadow pull in enemies then switch to [Sevagoth] to nuke with 2 then 1, now with Condemn i can fill my overshields entirely with one cast on a massive group then any survivors after nuking you can kill with headshots while they are immobilized by condemn procing Arcane Victory for health [Regen] that you probably won't need due to plenty of shield and Adaption. With this set up you won't even need your passive.
I don't have Condemn!
If you don't have condemn, Gloom is still really good and actually more useful if you go deep into steel path but for casual play i find Condemn more fun, another option is [Hildryn]'s Pillage however if running this i recommend replacing Arcane Victory with Arcane Grace.
[Natural Talent] is also worth mentioning as a replacement for [Stretch] due to less rang being needed seeing as they are in a cluster from shadow pull, [Natural Talent] allows you to switch forms faster and obviously do ur combo faster.