The Umbral Dragon's [Fury]

A build centred around huge amounts of power strength without sacrificing efficiency for the use of Gloom as a subsumed ability, this setup focuses on performing well in endurance runs & steel path content with ease!

With the use of [Combat Discipline] we can achieve an easy synergy with the bonus weapon damage on his 3rd ability as well as helping to proc Arcane Avenger.
For our power strength options, we have taken [Transient Fortitude] for the extra strength over less duration, this is used instead of [Blind Rage] to keep the efficiency at 100% as well as [Umbral Intensify] , Auger Secrets (note: this also helps to shield gate without [Brief Respite]!) & [Energy Conversion] (this is used to proc the max cap slow for Gloom & help with casting his 3rd ability on first use).

We use [Stretch] here for the extra range on gloom to allow for more tilesets & rooms to be utilised effectively & [Cunning Drift] to add some more onto that too! you can replace this with [Power Drift] if you like although it will only benefit the 3rd & 2nd ability a little more, there's no point in using it for more slow on gloom as we already hit the max cap with the mods selected. ether way you can replace the exilus mod with any mod although some selections may depend on you requiring an umbral forma (e.g [Primed Sure Footed])

At this point you are left with selecting [Rolling Guard] or [Adaptation], considering the slow amount of [Rolling Guard] & how much armor you get from using both your 2nd & 3rd ability while toggled with Ice, i'd recommend [Rolling Guard] to Remove Status Effects as this is the only weakness to the build, As an alternative you can replace [Stretch] with [Adaptation] for more tankiness and this will help a bit with survivability but considering the slow of gloom, [Rolling Guard] is the best choice here!