for agatha, get the spiced falcosaur omolet food (it works for agatha)
stack as much mastery as u can, u need to be able to aoe adds quickly.
for talents use: 3 3 2 3 1 2 1
pop army, lust and potion (unbrided fury (BFA) or prolonged power from legion), unh blight, DT, apocalypse, all your opening now. you will be able to army later anyway and maybe an extra pot.
healing imps will spawn i think 15 secs on the fight, its important u notice them as they spawn and swap, chains of ice one and dps the other as he runs, when he starts to cast use death grip to interrupt (use the talent that resets death grip on kills) and finish him off, repeat for the other imp.
use a button to command ur pet to attack the imp ur killing
exploding imps, kill them if nothing else is on the map, grip to interrupt cast so they dont leave pools, kill resets grip, dont stand still so he has to keep running and doesnt start the cast
after the first burst, always save blight+DT for the invulnerability imps, they spawn every min so you should have it up always, use outbreak to spread virulent for epidemic the rest of the times
the caster imps just DnD cleave and epidemic
shield was breaking fairly easily so i used apocalypse on CD, save interrupt for agatha always
ADDS >> agatha, she will get cleaved down steadily
at 35% spam soul reaper, with mastery it will hit like a truck
seed pod from emerald nightmare first boss is good to help aoe imps when u dont have DT, also deals good dmg on boss
if u got the heirloom trinket vs demons u can use it
mechanical dragonling (14 ghost iron bars and 12 cloth) is also great dmg in single target and aoe, and u can socket it with 24 haste and 12 mastery with special cog gems
good luck
edit, at start position urself on ramp so u can see the healing imps spawn and act preemptively. on rise try to be sideways so u can look at bolders and imps, same at the bottom