So, I have a Slyph (Dark Armour/Kinetic Melee)

[Major_Decoy]

I made an air elemental, Dark Armour tinted to look like clouds, and I have build, and it's okay, but I have this urge to fit Whirlwind in, now that I've remembered it exists. I'm pretty sure I could drop enough powers to fit Whirlwind without hurting my build terribly, but... there's absolutely no way I'd have enough endurance to actually run Whirlwind, is there?

[Psyonico]

Well, there's always Conserve Power/Physical Perfection and Miracle/Numina's/Panacea procs.  If you're still tight for endurance, there's Ageless Core from Incarnate.

[Sovera]

17 hours ago, Major_Decoy said:

I made an air elemental, Dark Armour tinted to look like clouds, and I have build, and it's okay, but I have this urge to fit Whirlwind in, now that I've remembered it exists. I'm pretty sure I could drop enough powers to fit Whirlwind without hurting my build terribly, but... there's absolutely no way I'd have enough endurance to actually run Whirlwind, is there?

Not with Dark Armor, no. With the Auras in the Tailor you can make a character that is surrounded by crackling thunder clouds so you need not be tied to Dark Armor. Something like Rad Armor would have all the endurance you'd need to run Whirlwind.

[Justaris]

Most of Dark Armor's bad reputation for being an endurance hog comes from two powers - Death Shroud and Cloak of Fear.    It's unlikely you'd want to run either of these toggles at the same time as Whirlwind since you'd be knocking the targets away, so actually I think with appropriate endurance reduction in the armor powers and in Stamina this is entirely doable.    Make sure to slot a Theft of Essence proc in Dark Regeneration to cover the endurance costs there.

 

[Major_Decoy]

With Sudden Acceleration I don't think I'd be knocking anything away. It's just that Whirlwind has a truly obscene endurance cost.

[Justaris]

If you're using Sudden Acceleration or Overwhelming Force to mitigate the knockback then you might get some value from those auras after all, but unless you're building specifically for endurance management you'll have a tough time running all the toggles as those two alone are responsible for scaring people away from the set as an endurance hog - add in Whirlwind and you'll likely need to counterbalance that equation with a lot of endurance recovery and management tools.    It's doable but it'll need to be at least a minor focus if not the entire focus of your build.    Cardiac alpha, Numina/Miracle/Panacea/Performance Shifters, Ageless destiny, Conserve Power / Physical Perfection from the Energy Mastery epic - you'll want most if not all of those.