Ah, this type of nagato build, with the passive paths of pain so people don't have to micro. I was making one of these, before I was told they just wanted the Gravity based Pain.
#1. 300 units is like... nothing. Just so ya know. Mana drain needs to be scaled, since 100 mana for 2 units at level 1 is pretty game breaking.
#2. Why does it have a radius? Isn't this a just a single target spell? Anyway, seems interesting.
#3. Hidden Rain Ninjutsu XD. Welp...does this follow Nagato, or stay put? Seems kinda okay, if the hero had a means like Enigma to keep people in one spot. The build doesn't have that type of spell, idk how effective it will be.
#4. Immediately, the CD is kinda off. Given the immense power these summons have, the CD needs to be quite long.
And the Pains, seems like you're missing two? Well, since you're delving into Invoker territory with this number of spells I already see one potential problem with your build and that is you can use all of these spells at once! I would perhaps suggest giving the hero the option to toggle between Pain bodies to choose one spell to use every X seconds. Since, some of the spells are quite powerful. It would mean changing up your build, maybe, depends on if you want to keep the summoning aspect. That could still work as in you toggle to the Pain you want, summon him and if he dies he cannot be summoned until X seconds has passed or unless you use the King of Hell unit. And you could switch to another Pain after X seconds as well, unsummoning the currently summoned one. Although, seems like it would be complicated. I used a similar solution on a hero suggestion I'm making for another game, when I ran into a way of a hero with many spells, but I didn't want to use the Invoker mechanic of essences or w/e.
Pain #1: So do you do use the spell, or does the summoned unit use it randomly, or when certain conditions are met?
Pain #2: 40% is quite high in the early game, which is when you gain this unit. I would reduce it to around 25%.
Pain #3: Er... a little strong for my liking, especially the disarm component.
Pain #4: Good idea, I suppose. Although, I would make the CD for its revive spell a little longer.
Edit: My idea on your ultimate would look like....
Six Paths of Pain- Spoiler:
Nagato gains two spells: The Paths of Pain (A Toggle-able-Passive) and Summon, an active spell.
The Paths of Pain allows Nagato to Toggle Between the Pains available, ideally if a Pain unit was dead their icon would indicate that. Or, a player can type a command to see which ones are alive.
Summons allows the player the summon a Pain every X seconds. If a Pain dies they come back to life after 80 / 70 / 60 seconds.
Note: When a Pain is summoned he appears right infront of you, in the direction you were facing. When you use Summon the current Pain will become unsummoned and replaced by the new one. Additionally, you cannot try to resummon the same Pain.
Activation Type: Self Position
Type: Magic
Cast Time: 1.0 seconds
Manacost: 80
CD: 50 / 40 / 30 seconds