Emma has always been one of the most slept on heroes in the game. She is also my favourite character to play with since her rotation is easy to use and her damage potential can be absurd. And she can be nearly unkillable due how tanky she is with the right setup. My highest brutal hit with her in patrols while in a group is 14mil on signature...

This build works great in both solo and group play.

Since we have enough damage to oneshot almost all terminal and some Patrol bosses with our Signature ability, if the Brutal Hits are generous, this build works well with both The Warlock's Eye and Shield of Perseus. I personally use both, depending on what I am doing in the game. 

Her rotation is quiet simple really: 
> >  > >  > . This can all be used under 2 seconds and it provides a One Shot effect on 90% of the Cosmic Terminal Bosses if you are doing them solo and depending on your party insignias, it can also one shot or delete 90% of the boss hp if you are in a group. Only exception to this is of course Dr. Doom, since he has huge amount of HP and 3 phases...

After that rotation you can dash out with Furious Lunge(dont use it to soon, it sometimes cancels your signature-wait untill you have dealt the damage with Kneel Before Me first!) follow up with Psychic Spear or if you want, you can replace your spammable filler with Drain Psyche on left click hold, it deals great amount of damage and provides survivability as well if you need it(or short on IP's). With that gear setup, we have more than enough Spirit regeneration to sustain it while holding it.

If you are planning to use Drain Psyche as a filler, make sure the 150hp regen on one of your cosmic artifacts is replaced with 10% cooldown on Signature while in combat.

Since all of our buffs/debufffs are on 8sec duration and cooldown, it all just works like a charm. The Perfection talent reduces our Signature everytime we use Show Off and Astral Whip( the 15% vulnerability from the Whip also stacks with the 10% we got from Telepathic Torment)  so everything we use compliments each other really well.

We in CoA have 50% global CDR, but the rotation stays absolutely the same for TAHITI as well.

If you are wondering if she is EDR capable(CoA), well yes indeed. Telepathic Illusion is one of the best CC/tanking abilities in the game, so bosses can just pretend that you do not exist while eat tons of damage from you. Kneel Before Me has such a LONG animation and you are invulnerable for 3 seconds, while regenerating hp/sp in it. That is why we want 1000 Defense rating on Signature use in our Catalyst. The moment the Signature is dealt the damage, dash out with a Lunge if you are in harms way, while having the extra defense the Catalyst provides.

You can replace Doctor Doom (Classic) Team-Up for Jessica Jones Team-Up if you want even more CC/grouping and brutal damage.  I personally switch between both. Both work really well with Emma. The Deadpool Kid is also an great option if you struggle with EDR

The ring is not what I use in game, but the website doesnt let us choose double Brutal chance and damage rating on Bloodstone Demonband so if you dont have one, use any of those   all work great with Emma really. For a cosmic one specifically, you want +3 Durability or Intelligence and above 1000 Brutal Damage Rating.

For trash mobs/adds you can just use Telepathic Torment, Sudden Dread and just move on, they will die offscreen. You can of course use Astral Whip and Show Off as well for even faster screen clearance and movement/positioning.

Here is an video of my Emma taking down Cosmic Juggernaut in 3 seconds, hope you enjoy!