Abilities and Explanations
Q (Enraged Battlecry) : This ability gives Magtheridon, as well as every ally in a large range, a small boost to their attacks, as well as reducing the damage enemies give. The amount in itself is small, but it gives VERY appreciable bonuses to Magtheridon's abilities. Do note that as long as Relentless charge extends the duration, allies still benefit from the buff, as Magtheridon is still, technically, under its effects. Might be worth to note that Magtheridon is still under the effects of the spell even if he doesn't benefit from its 5% extra damage, so it will still give its bonus to its abilities, if applicable.
W (Crush!) : This ability is a short range stun that deals a small amount of damage. It's pretty self explanatory -- You stun someone and deal damage. This ability, however, benefits from a bonus from your Q, and your ability damage from Fury of the Pit. But, added to all of that, is the auto attack bonus it consumes to give itself an even bigger bonus, that can get its damage to terrifying levels, for someone who is already low on health. This ability, due to its stack consuming effect, may be a good combo closer on Magtheridon (Battlecry, Charge in, shockwave, crush, etc.), to get the most out of his kit.
E (Cleaving Shockwave) : This ability hits everything in a medium length, but great width in front of Magtheridon, dealing great damage, benefitting from Fury of the Pit and Enraged Battlecry. This is also pretty self explanatory -- E in a direction, hits people, cleaves to other targets. Do note that an enemy hit by the big wave cannot be hit by a small, but the inverse is not true -- an enemy hit by a small wave that cleaved from behind a target can still be hit by the big wave.
Armies of Outland (R1) : This ability revolves around summoning very strong minions that make Magtheridon a real pushing force to be reckoned with -- You cannot set the focus of these minions, but they will hang around Magtheridon unless he dies, and deal LARGE amounts of damage, so much that, wether it's in a team fight or in a lane, they simply cannot be ignored. Using this, Magtheridon can effectively push a lane and fight "Alone" under towers without fearing to take damage from them, as long as his army is nearby. Upon dying, they're all healed, last forever, and push down the nearest lane, stronger than a regular wave of minions, which makes this ability VERY strong if your team lacks pushing, or has a Sylvanas (Who relies on minions to deal damage to the structures).
Rain of Chaos (R2) : A signature ability from pit lords in warcraft 3 -- This ability deals VERY appreciable damage, if it all hits. Sadly enough, it simply goes around randomly within a large area. This, however not always dealing the damage you wanted it to, will still prove quite effective, as it can make enemies fearful of continuing a team fight. With a relatively low cooldown, this ability, however, does not benefit from any boosts, while still being a very effective tool for scaring enemies away, as stealthed heroes will be revealed by the impact of the fire balls, or by the small burn effect they leave.
Special Mount [Z] (Relentless Charge) : This ability is Magtheridon's main way of being mobile, as well as being his only chase, his main engage and his main disengage, also stuns a hero when it hits one, as well as dealing damage that benefits from a lot of his boosts, as well as making his Enraged Battlecry's effects last longer for allies, and dealing more damage for himself. This ability is something you'll have to learn to se -- With a 45 seconds cooldown that recharges slower when you are not fighting, you'll spend your time fighting anything to be able to use it as soon as possible, as it is a fantastic tool to engage upon enemies, dealing high damage that can actually be quite scary for a fleeing squishy, it also gives you an instant bonus to your fury of the pit passive. Aside from all these effects, this ability pushes lane minions out of the way, stunning them for 1 second and dealing 30% of the ability's damage when it hits them.
This ability's cooldown is slower at recharging when out of combat, but Lane Minions hitting you, or you hitting them, makes i recharge normally. This ability can recharge up to 25% faster in team fights -- 5% faster recharge for every nearby enemy hero, and takedowns take instantly 5 seconds off.
Fury of the Pit [Passive, Trait] : Magtheridon's trait is central for Magtheridon's gameplay. The more you hit and get hit, the more you deal damage. Simple, very effective. A simple catch -- You HAVE to stay in battle. Magtheridon passively moves 5% slower than other heroes, so it will be very hard to move around, especially considering that he does not have a mount, so he will spend a lot of time out of combat, and that, reduces his trait's bonus very quickly. He can, however, interrupt the reducing of his trait's bonus with his enraged battlecry. His trait scales up... intricately, at the very least.
Damage over time (Such as envenom, and Sin's Grasp) do not make his trait proc. Damage tics (Like living's bomb damage tics before its explosion) do not trigger it, either.
He, however, gets the full worth of every baneling or every attack coming from a summon, and if it counts as ability damage, he gets the bonus for ability damage. Heroes with ability that hit a lot, Like Zagara, will have a hard time Laning against Magtheridon. Heroes that attack very fast, will have also a hard time against him.
Heroes that rely on big bursts, like Kael'Thas, won't have the hardest time against him, , as only primary damage (And only that) will proc his trait. Leoric, who does a lot of percentage damage, will be the most obvious and primary counter to him, as his drain hope is one specific ability that will only trigger his passive upon its last damage tic, along with living bomb, who only triggers it with its final explosion.
His Playstyle
Magtheridon is to be played as a very offensive character -- an extensive health pool allows him to stay in fights long enough to build his passive, which allows him to Q up, charge in, shockwave, then crush, and auto attack at will, which will be able to do an impressive amount of damage. I am not adding in the worth of auto attacks or of his ultimate ability, either. In this, I will describe what I would picture his early, mid and late game all-around-wise to be like.
The Early Game (Pre-10)
Magtheridon's early game should be to try and pin down which lane has the character that would be the worst against him. His teammates should play around him heavily, like they would to any solo tank, but have a very particuliar attention as to his needs : He needs heroes that don't have many stuns, so Johanna and Muradin, right off the bat, are out of question matchups for him. Heroes that will benefit his trait without him putting himself in danger too heavily. Leoric is a straight up no-no, and Kael'Thas could prove to be very problematic as well. An ideal matchup for Magtheridon would be to go up against Tychus or Zagara, maybe even an Illidan, but you rarely get those. So watching out for opponents swapping lanes to counter Magtheridon is a thing the allied team should be ready to do. Other than this, pushing lanes is not something particularly problematic for Magtheridon, so long as he stays clear of towers while his passive is active.
The Mid-Game (Post-10)
In this stage of the game, Magtheridon's time to shine or to crash has come -- an enemy team with a lot of stun, or abilities with a lot of damage but few casts will be his ruin, but he will truly shine when enemies focus him a lot when a healer is keeping him alive, as Magtheridon has a massive health pool. At this stage of the game, you have your ultimate ability, which should tell your team what you will be focusing on doing : Team fighting, or Lane Pushing. Magtheridon can, in fact, be good at both, and his "Armies of Outland!" heroic ability can allow him to push past towers and forts VERY easily if left alone, as well as massing up minions waves of his own. If you took the "Rain of Chaos" heroic ability instead, you will be focusing around making sure the area your team is fighting in is advantaging them, instead of focusing on single targets. You would also be focusing very heavily on staying in the front and peeling for your allies, which brings both a problem and a good thing : Magtheridon's massive hitbox. Magtheridon has a HUGE hitbox, which allows him to block his enemie's paths and peel for allies very effectively, if positioned right. However, it makes it difficult to avoid stuns and skillshots, due to the mentioned before massive hitbox. It should be something to be very careful about when playing Magtheridon, as the enemy team can very easily get their skillshots on you, but can also miss your allies due to you blocking them. Wether or not you play it to your advantage is up to your skill level and how you play Magtheridon all around.
In this stage, you may have up to the keeps pushed, or maybe up to the forts and past them on one lane. Map objectives is probably something your team will want you to focus upon, and so, you will need to build accordingly for what your team demands of you, as Magtheridon is a character who weighs heavy on the game. He can be a game changer for both camps, depending on how it plays out.
The Late Game (Around Level 20)
At this stage of the game, you quite probably have your keeps pushed down or nearly, and have pushed the keeps down, or nearly so, on both teams. That said, you also have your level 20 talents, that can be game changing, at his level range.
If you chose to go lane-pushing, you make your summons a lot better, and get to keep, as long as he's alive, the middle piece, which is either a Doomguard or a Warlock, both of which are excellent, as they will soak tower shots for you, while you damage (quite heavily) the enemy's structures.
If you chose to upgrade your "Rain of Chaos" ability, you now have a charge on it that has a 50 second cooldown, as well as having it empowered. It can be cast without the charge up, but you won't summon the (very powerful) Infernal, that has massive health, very large amounts of damage, while not lasting very long. Your meteors also leave a small trail of fire where they landed, which deals damage -- always practical. At this level range, the Infernal can also be used for pushing down the last structures, if needed, as it can soak up large amounts of shots, or deal large amounts of damage, when summoned.
If you chose to go with the "Brutallus" final talent, you basically get to micro-manage a mini yourself for up to 60 seconds. The mini you goes passively 10% faster than other heroes, only has the cleaving shockwave, and has a new trait, while not possessing a mount, and only having 40% of your stats (except for attack speed, which is, thankfully, a little higher -- 1.09, to be precise.). The trait seems quite good upon first look, but don't be delusional -- Brutallus is there to allow you to have some presence even while dead, and to basically make you teleport after resurrecting, due to your slow movement speed. Brutallus has only 40% of your hp, which isn't too high -- it's only around 3450, at level 20, which is pretty low. Brutallus, however, does have 160% of your auto attack damage, instead of having 40% of it, due to Magtheridon's very low damage before stacked up.
And, for the final choice, you have "Truly Relentless", which makes you a real MONSTER to be reckoned with. If you are good at landing your relentless charges on heroes, you can basically be casting them all the time. You can get up to an instant 28 seconds reduction on your charge if you kill the hero you impacted with, which leaves it with a very short 17 seconds cooldown that can recharge up to 20% faster, making it recharge at a rate of 1.20 (which is 1.12, if you turn to 2 at 1.60) per second. But it ALSO makes the stun longer and makes the impactee vulnerable, which is very appreciable, as always.
Your final talent choice may very well impact the outcome of the game, as Magtheridon is a hero that, at default of having a lot of mobility, has to focus on being VERY strong at one place, rather than being everywhere while being a little less strong, so affirming your presence where you are is going to be a must if you are to play Magtheridon.
Heroes of the Storm Build Guides
Also, if you are speaking of how Mannoroth dies in Warlords of Draenor -- I wouldn't add it myself, as it would be too "Tyrael-ish". That explosion when dying is also Mannoroth's signature -- No other pit lord, if you would check, dies that way, might it be in WoW or Warcraft 3. As much as it sounds appealing, I'd like to let characters keep things that are belonging to them -- Tyrael exploding when he dies after moving a bit, Mannoroth exploding on the spot, etc.
How does crush work on heroes that are as big or just a little bit smaller then Magtheridon. Also how does it work if somebody is also playing him. What happens then?
Besides that, you have a very promising concept of a hero that just hits harder and harder the longer you try to fight. So props to you. :)
I don't intend for him to actually pick up the target and crush their ribcage, I instead would have him simply do a punch-like animation towards the target, as picking up the target to crush it would be a little complicated with big heroes, as you said.
Thanks for reading my concept, I'm appreciative of any feedback!
Besides that, you have a very promising concept of a hero that just hits harder and harder the longer you try to fight. So props to you. :)