If an enemy dies within 4 seconds of Muzen'Khan damaging them, a number of Koglings will spawn from their corpse. Koglings will seek out nearby enemies (prioritizing champions) and will explode after 4 seconds, dealing 20 + (5 - 10 (based on level) × level) true damage to enemies within a 175-radius area and slowing them by 20% (+2.5% per 100 AP) for 2 seconds.
Koglings will prefer to target unique enemies and enemies will take only 50% damage from concurrent Koglings within a 4 second period.
Enemies damaged by Muzen'Khan receive a cosmetic debuff to indicate that you will explode on-death.
Passive: Muzen'Khan's basic attacks apply between 1 and 5 stacks of Corrosion to his target based on the amount of time since his last attack, applying maximum stacks after 10 seconds. Each stack of Corrosion deals magic damage per second and reduces the target's armor by 5% for 3 seconds, stacking up to 5 times.
Hitting enemies marked with Corrosion, Terror or Murk will spread the debuffs to all enemies in an 400-length cone behind the afflicted enemy. This does not refresh the duration of extent debuffs.
Muzen'Khan hungers for magic.
Passive: Muzen'Khan gains vision of enemy champions within 1500 / 2375 / 3250 / 4125 / 5000 units for 3 seconds whenever they activate an ability. Enemies within 1500 units of Muzen'Khan will be altered that he can see them.
Passive: Whenever an enemy champion within X units expends mana, Muzen'Khan compels it toward him - restoring health equal to 15 / 30 / 45 / 60 / 75 % of the mana spent.
Active: Muzen'Khan takes to the skies, becoming untargetable and gaining the ability to ignore terrain collision for the next 3 seconds. When Muzen'Khan descends, he terrifies all enemies within a 125-radius area - causing them to turn and flee for a short duration.
Fear Duration: 0.25 / 0.5 / 0.75 / 1 / 1.25 (+0.1 per 150 max health)
Muzen'Khan will cast a shadow on the ground while moving, and his map icon is still visible.
Fun Idea - Flee now affects minions and monsters differently to champions. Minions and monsters affected by flee do not run directly away from their source, but instead lose their ability to differentiate friend from foe. Upon being feared minions and monsters will lose their current attack target and immediately move onto attacking the closest nearby target. The feared minion/monster could gain bonus attack speed or alternate between targets without needing to kill them first.
Active: Muzen'Khan spits of globule of toxin forward in the a line that deals magic damage and applies Murk to the first enemy hit. Murk reduces the target's vision radius to 675 and removes their allied vision for 3 seconds.
Active: Muzen'Khan swallows the target enemy, suppressing them and rendering them untargetable. For the next 1.5 seconds, Muzen'Khan gains the ability to cast Reflux again, his movement speed is drastically reduced and he cannot attack or cast.
Active: Muzen'Khan spits the swallowed enemy at the target area, dealing magic damage and knocking up all enemies within a 255-radius area on impact for 1 second. This is with the exception of the swallowed enemy, who is slowed by 99% for 2 seconds instead of being knocked up. The slow decays down to 0% (+10% per 100 AP) over the duration.
As a ranged support he features a laning pattern similar to Thresh: harassing with basic attacks, while needing to get into the fray in order to use his abilities.
Marking minions with Death Throes and then allowing his carry to kill them generates free harass, although bad timing/aiming will lead to pushing the lane. I'm tempted to add bonus damage against minions to exaggerate this weakness. Saying that, intentionally marking an entire minion wave and then having your caster/carry clear it will spawn an army of Koglings with only champions as a target.
I'm not satisfied with how Acid Slash spreads the debuffs. In my mind, Muzen'Khan is performing a Decimate-like animation with his claws and the debuffs are spread around due to cross-contamination. I want to make it a slow sweep, but Riot's stated this is fake counter-play (since it'll either sweep too slowly to ever land it; or too quickly that the fact you can dodge it is meaningless). I'm tempted to go for a Diana/Thresh hybrid, where it's a large arc (either from the left or right depending on if its aimed from the left or right of Muzen's middle) and it "picks up" debuffs when it hits people and carries them to everyone else you hit - clipping someone with Acid Slash at max range won't do anything. It needs Flay-like reach.
I can't decided if Muzen'Khan's fear should scale with maximum health or a bonus health scaling - the total duration at maximum build should be the same, but should there be per level?
If Riot cannot animate his basic attacks to look distinct from Kog'Maw's while still being fluid - switch them for barbs or spines (Muzen can either spit them, or he can have a stinger - he currently has a hole in the end of his tail). As with Thresh, he would have different attack animations based on proximity to the target.
I'm tempted to change my stance on Acid Slash refreshing the durations - perhaps "Acid Slash will increase the remaining duration of any debuffs by 1", or by (0.5 seconds per 100 AP). This might have an issue on URF, but maybe have it capped at a number of additional seconds - or only have it refreshable once.
The beautiful thing about insects (such as bees and ants) is that larva, males and females have such distinctive appearances, you can keep re-using the theme without actually overlapping. Perhaps Kog'Maw needs a mother? A queen-mother.
Passive: Muzen'Khan's basic attacks deal splash damage in crescent-shaped waves; alternating between left and right swings. On-hit effects are only applied to Muzen'Khan's target. Striking an enemy marked with Corrosion, Terror or Murk will spread the effects to all subsequent enemies damaged.
Splash Damage: 50 + (3 * level) + (50% bonus AD)
Active: Muzen'Khan channels for 0.75 seconds, spitting 5 globules of acid at the cursor at regular intervals. Each globule deals magic damage and applies Corrosion to enemies in each of the target areas and singes the floor for 1 second, causing enemies who remain in the air to generate Corrosion stacks at 0.25 second intervals. Corrosion reduces the target's armor by 3% per stack for 4 seconds, stacking up to 10 times.
Active: After channeling for 1.5 seconds Muzen'Khan takes to the skies, becoming untargetable and gaining the ability to move through terrain. While in flight, Muzen'Khan leaves a shadow on the ground below him and cannot use basic attacks, abilities or item actives. At the end of the ability's duration or upon casting the ability again, Muzen'Khan dives to the location of his shadow after a 0.5-second delay, dealing true damage in a 250-radius area.
Flight Duration: 6 / 8 / 10
True Damage: 300 / 475 / 650 (+ 70% AP)
"Muzen'Khan" is a play on words; being both phonetically similar to Ah Muzen Cab, the Mayan god of Bees, and containing the Turkish/Mongolian word meaning "King". Literally it translates to "God King", since "Cab" is the Mayan word for "bee", but don't look into it too closely.