You no have any.
I could suggest some.
Health: 480 +90 per level. (160 + 30 per level each)
Health Regen: 7.5 + .75 per level
Energy Regen: 25 per 5 seconds.
Attack Damage: 53 + 3.8 per level.
Attack Speed: 0.600 (+ 1.5% per level). That's basically .200 + .5% per level for each of them.
Armor: 12 + 3 per level.
Magic Resist: 30 + 1.25 per level.
Movement Speed: 305
Passive - Insatiable Hunger
Their attack damage against the same target could increase by 5/10/15 each time, perhaps? Up to a maximum of 20/40/60 total extra? With this ability, I would advise low base Attack Speed for the stats. The attacks between each of the beasts should cycle. And Omen's can't be 10/25/30. It would need to be 10/20/30, since it has to scale evenly. You don't need to describe when they upgrade, the game does that on it's own. Qualm's could add 2/2.5/3% of maximum health, and Gevaar's could add 20/30/40% of AP. However, I also have another suggestion. Once the Swam reaches 67% of it's health, Gevaar 'dies'. Once it reaches 34%, Qualm does too. If you survive, and heal, then a void portal opens for a short amount of time, and they rejoin you. This would balance out the strength of your passive here. The refund seems fine.
Q Ability - Omen of Agony
I would say 50/100/150/200/250 damage, plus .5 AD would work. It could last for 5 seconds I would say. but 1.5% is tiny...perhaps the Swarm gains 10/12.5/15/17.5/20% Armor and Magic Penetration for 3 seconds or so? How long does Crippling Bite last? This is a matter of opinion of course, but I would suggest calling it Hamstring(the act of cutting the hamstring). Damage could be 35/75/115/155/195, plus .3 AD, since it has the slow effect. Rend might deal 8/11/14/17/20% as damage(not all of which would affect them due to armor). I assume the 150% means of AD, in which case you should say so, and 1/1.5/2/2.5/3 would work. Or just a flat 2 seconds, in which case the AD should scale with leve(120/135/150/165/180%?) Cleave should have a limit on the number of times it can be used, based on level, and should affect one foe at a time, otherwise far too powerful(lots of damage there, you know). Like a very short range skillshot, and if it hits, he can use it again within the next second. Up to 2/3/4/5/6 times. The whole ability could have a normal cooldown of 20/19/18/17/16 seconds, with an energy cost of 25 for all of them save the first, which costs 40. Effective range, for any of the abilities, should be quite short, about 250 for all of them except Omen of Agony. That should have a range of maybe, 400?
W Ability - Sentiment of Fear
Ouch, true damage...hmmm...maybe 20/50/80/110/140 + .2 AP. True damage is pretty powerful. And there's only Tenacity for the reduction by the way. I suggest 5 seconds, but the Tenacity reduction scales with level. 20/25/30/35/40%, perhaps(but meaning it reduces the effect of the tenacity)? If they don't have Tenacity, then that would mean the CC would last that much longer. Screech could double the magic resist reduction, and deal the same amount of damage as Herpetaphobia(I'll do that later). Though I don't know why it's called Screech if he just stares...Ferocious bite could do more or less the same thing, doubling the vulnerability, and dealing 30/60/90/120/150 +.3 AD true damage(60% of the damage Omen of Agony deals, basically). Discharge seems a lot like Spell Flux, so I suggest it bounces up to four times, if there isn't more than one enemy, it simply does triple the single hit damage. The enemies would have to be within say 250 units of each other, and the balls speed is 750. It would deal perhaps, 20/45/70/95/120 damage each hit? And if a target dies, they deal 50/75/100/125/150 damage to all enemies within 200 units of them. Gaping Wound could deal 50/90/130/170/210 damage, and another 30/55/80/105/130 damage over 4 seconds. The range, cost, and cooldown would be the same as your Q ability, except for Discharge and screech, which would have a range of 400.
E Ability - Herpetaphobia
Damage for the first ability could be 60/70/80/90/100, but the amount of MR reduce would be a number, and increase much more. 15/30/45/60/75 MR reduce. Hehehehehe...Infection should deal a good amount of damage, say 80/100/120/140/160 but over a very long amount of time. 7 seconds, and they have to be within 300 units of an allied unit for 2 seconds continuously to spread the infection. And they can get the infection back. And it can affect minions, so a very good AoE DoT ability, even without being there often. Bad Breath might deal 50/110/170/230/290 damage, and silence for 2 seconds. Energizing Roar could increase the AS and MS by say, 30/35/40/45/50% for 3 seconds. Nausea would increase the cooldowns by, say, 30/40/50/60/70% for any abilities used withing the next four seconds. Enemies affected would be in a 80 degree cone going for 600 units. Other than that, Cost, range, and cooldown would be the same as Q.
R Ability - Dark Swarm
The passive is nice, but too powerful. That's making every 4 attacks equal to 4.5 at first getting this, into 5.25 at the next level, and into 6 at the last. AND an energy refund? No. Master Yi's passive increases every 7th attack into 8, not every 8 into 9, then 10.5, and then 12. As a straight comparison, the ratio is 63:72, while yours would be 64:72(Master Yi has slightly better at this point), then a comparison ratio of 147:168 to a ratio of 124:168(yours is better now), and finally a ratio of 14:16 to 14:21(far better now,with an energy refund too!) No. Every 4th attack is good, and fine, but a lower percentage. Maybe 50/60/70%. And a lower energy refund that scales properly. Like 5/10/15 or so. Anyway. On to the active. I'm going to actually review this, not just suggest numbers. I would think the extra voidbeasts would simply increase the attack speed by...a lot. The energy seems fine, so I'm going to suggest numbers now. 50/75/100 (+.2 AD/+.3 AP) physical damage per attack, but it summons two each time, and it increases attack speed by 66%(up to 1.000 not counting anything else, like level.), and causes it to cycle between all of them. It also adds max/temp health, maybe, and once that health is gone, the beasts disappear? Just an idea. It could add 300/500/700, maybe? The void energy could deal 20/50/80 (+.05 AP) true damage to enemies within 100 per second as long as the ability's active.
I really like the idea, and am going to do something in a subsequent post for possible lore and other things. Just suggestions, mind you, though.