Complete and utter waste of time to do Sky on anything other than d0.
For lulz I did Sky on higher difficulties today. On D2 every boss was double class, meaning their HP was about 1.7x. I was getting moon and triangle motes.
On Sky D4 the bosses are mostly tri-class, and their HP is about 2.35x in my log. I just failed to do Overseer because he spawned as a magician. I couldn't dispel his DS because of his level, so I took about 11,500 DS damage and lost the fight at 5%. So next attempt I waited until the DS was about to fade before engaging. Mid-fight a blue drake from isle 7 flew inside the windmill spinstunned me ensuring my quick death.
Do befallen on a twink and get 10 square motes an hour if you want motes. For some reason they want this to be the best solo mote farm, unless you're a bard then you do insane AoE damage and farm d4 planes. Upgrade your sky stuff with level 10 befallen drops.
Sky on D1+ is a complete waste of time