Explain Outworld Devourer's Sanity's Eclipse (Ulti)

There's stats called strength, intelligence, and agility for each hero. These stats determine other things about the hero (their attack damage, attack speed, hit points, armor, etc.)
The ultimate of Outworld Devourer looks at the total intelligence of the hero casting it (Outworld Devourer himself) and then does the following for each hero in the AOE:
If the other hero's intelligence is higher than Outworld Devourer's, it does nothing.

If the Outworld Devourer's intelligence is less than (10/30/50) more than than the other hero, the other hero takes the difference between their intelligence times (8/9/10) in magical damage and loses 75% of their current mana
If the Outworld Devourer's intelligence is more than (10/30/50)+the enemy hero's intelligence, then it just does the difference between intelligences times (8/9/10) damage.
If the other hero has magic immunity from Lifestealer's Rage, Omniknight's Repel, or the item Black King Bar, they can get their mana reduced by the 75% if they fall in that range, but they will NOT take magic damage from it.

Examples:

Outworld Devourer has 80 intelligence after items etc. He lvl 1 Sanity's Eclipse a Pugna with 100 intelligence. Because Pugna's intelligence is greater than Outworld Devourer's, the spell does nothing.
Outworld Devourer has 80 intelligence after items etc. He level 1 Sanity's Eclipse a lina with which had 782 mana currently of a max of 1288, with 76 intelligence before Outworld Devourer's Sanity's Eclipse hit her. It does (80-76)*8=32 magical damage, and since the difference in intelligence is low (less than 10) it also drains .75*782 mana leaving lina with 195.5 mana.
Outworld Devourer has 200 intelligence after items etc. He level 3 Sanity's Eclipse a Phantom Assassin with 40 intelligence. She takes (200-40)*10 = 1,600 magical damage.

Against heros with slightly less intelligence than you it takes most of their mana, against heros with a lot less intelligence than you it does a crapton of magic damage that is blocked by Black King Bar, and against heros with more intelligence than you it does fuck-all. It can and will do different things to different heros caught in the aoe - you can one-shot a hero while another hero takes no damage in the same spell.

As Outworld Devourer you are best off mid, preferably having picked Outworld Devourer into an enemy int mid or hero that requires mana to do stuff mid. Outworld Devourer beats almost all mids hands-down except maybe Kunkka or Viper or Razor. In a normal 1v1 mid laning situation against most heros, every time the enemy hero tries to do anything - last hit, approach creep line, whatever - you want to cast your Astral Imprisonment on them. You get mana and intelligence from casting it so it doesn't hurt you to do so much. And you get attack damage to last hit better while crippling their ability to do anything (even attack if they are intelligence)

In fights, one of the best thing to do is to use it to set up other things from your allies. The little inner ring expands until it hits the outer ring exactly when the imprisonment ends; this lets you time disables to chain onto whoever was trapped in it. Explain that to your allies if you have people missing their disables as people come out of imprisonment. Good heros with disables that are otherwise tough to land because of their targetting and delay that can become easy to land with an imprisonment and timing include: