Sanity Break: Cthulhu sends out a terrifying blast of energy, dealing damage to all enemies hit and reducing their Attack Speed. Enemies hit by this ability also do reduced damage to Cthulhu for 6s.
This ability applies 1 stack of Torment, 2 if the enemy hit is facing Cthulhu or Fears them instead if they are afflicted with Insanity. Successfully consuming Insanity permanently increases the base mitigation of this ability.
Ability Type: Cone, Fear, Damage
Damage:
100 /
150 /
200 /
250 /
300 (+40% of your Magical Power)
Attack Speed Slow:
20 /
22.5 /
25 /
27.5 /
30% for 3s
Fear Duration: 1.5s
Damage Mitigation: 20% + 0.5% (Max 30%)
Cost: 60
Cooldown: 10s
Sever (Ultimate Form): Cthulhu swipes down at the ground beneath him, creating 3 large projectiles. These projectiles damage enemies and apply a stacking Protection Reduction debuff. This ability does not proc item effects.
Ability Type: Line, Debuff, Damage
Damage:
100 /
140 /
180 /
220 /
260 (+25% of your Magical Power)
Protection Reduction: 4% stacking up to 4 times
Debuff Duration: 5s
Cost: 0
Cooldown: 1s
His two, the mire field it leaves lasts for an additional 3 seconds after the ability is cancelled or ended but the damage aspect of it is only 2 shots. unless I am reading it wrong on how it works it only does the slow for the 3 seconds after the end of the ability. with no extra damage, so even then thinking about it i don't know that it would be that useful.
On the ult, again from my interpretation, all of his abilities in ult form only do 1 hit and whatever affect they do with that single hit.
If i am not mistaken, iso you really only want on gods that do continuous ticks like posieden with his ult and pool, or ares with his chains, fire or other gods with continuous damage, especially seeing as how it got nerfed from the 2 sec slow to the 1 sec slow.
Gem of Isolation isn't something I'd consider core on him. Barely even situational, if what I've tested is accurate.
So the slow would apply for a short while with his 1. If you get the first hit on his 2, the Iso slow can help confirm the 2nd hit, which means it can be somewhat useful there. It'll apply like normal on his 3 and ult. And it'll apply like normal in ult form on his 2 and 3. But except for his normal form 2, these are all very temporary slows, with no ticking or DoT damage to really make it effective and worthwhile.
The biggest question I had was applying the slow on his 1 in ult form. However, in jungle practice, I did a quick test on the moving Odin bot, and it didn't look like it applies the slow. Even though the 1 is technically an ability, you also cast it via standard basic, and I think the game considers it a basic. If it applied the slow, that would be nice, but since it doesn't (at least to my eye)...it just doesn't seem like a great pick to me.
Other than Iso, Ethereal Staff is built way too early in this build, Mantle of Discord is also too early IMO, and agreed that Urchin is too late (and I wouldn't get Urchin in a Support role personally).