- As a general rule, no stun should last longer than 2 seconds
Yeah I've said the same since the begining. Maybe 2.5sec would be alright. But 3 is so long. But frost nova and boulder roll are the only ones breaking this "rule" right now.
Boulder roll should stop at 2.5 sec and gain a 7 second cripple after the stun ends. Frost Nova should gain some other effect at level 3 instead of a 3rd second.
- As a general rule, snares should cap at -25% movement speed (snares should not stack beyond that point).
33% should be fine. 25% would be overdoing it. The problems we're having now is hte 45% and 55% slows.. Should try a 33% cap and see how that works, it'll probably be fine.
- Silence should not last longer than 5 seconds.
The 6 second silence is fine I think..
- Roots should not last longer than 6 seconds.
Currently.. no roots. A nd I don't liek your suggestions below on what should root.
- Stacking of CC should be limited by adding immunity timers. After a player has been stunned, they get a buff that makes them immune to CC effects of the same type for a certain amount of time. A good amount would probably be 5-10 seconds. So, for example, if you're stunned, you can't be stunned again for 5-10 seconds, but you can be rooted or silenced. This shouldn't apply to snares because of the amount of passive snares in the game that are reapplied automatically with each attack. Limiting snares to -25% should be sufficient as a general balancing move.
Unnessisary.. I think people are overreacting wanting these type things. You just simply shouldn't be able to be stunned while you're already stunned.
- Frost Nova and Mass Charm should be changed from stuns to PBAoE Roots. Players can still use skills, attack, etc, they simply can't move. Given that Frost TBs can already extend cooldowns and slow enemies, changing the stun to a root seems more than fair. Erebus is certainly not deserving of a nerf, but lowering the mana cost and cast time of this ability while increasing the radius will make Mass Charm still a very useful skill.
Overdoing it.

Just changing Frost nova to 1.5sec cast instead of 0.9 and reducing the duration to 2 or 2.5 seconds would be fine.
There is nothing wrong with Mass charm.. If anything, it needs a buff. What is the point of making Mass charm root? If it's root, then once you cast it someone else will use a stun on you, so they can attack you and use skills while in place, while you're stunned..
- Boulder Roll stays a stun, but stuns for a much shorter time (.5-1 second) and snares / reduces attack speed for a longer period afterwards. Yeah, this will make it a lot harder to do Boulder Roll + Hammer Smash, and more difficult to coordinate team ganks with a ranged stun. My answer: GOOD. Finally.
The 4 second stun is too long.. But like I said "Boulder roll should stop at 2.5 sec and gain a 7 second cripple after the stun ends.".
UB Grasp, since it holds the UB in one place, can stay the same.
Yeah. If anything, UB grasp doesn't heal enough, since it makes him sooo vulnerable. His grasp definitely isn't what makes him good, it's the other things, but it's not bad, and buffing it without nerfing something else would make him too good. So no sense bothering now.