The Pain Master is mainly a support hero even tough he can be a quite effective nuker. He has a good mix of defensive and offensive spell. The spell Share the Pain is the main skill of Pain Master, it can be used either defensively or offensively which make him a versatile hero on which you could focus to go all for offensive ability or defensive ability.
Share the pain with either and ally or an enemy. When casted on an enemy, this enemy will be dealt magic damage equals to the damage the Pain Master will receive multiply by (0.5/0.7/0.9/1.1). When casted on an ally, reduce all incomming damage by (35%/40%/45%/50%) of the target ally and deals (100%/95%/90%/85%) of the reduce damage to the Pain Master. Effect last 3/4/5/6 seconds and it will fade if the sight is lost or the enemy/ally is more then 800 unit away.
Mana - 100
Cooldown - 30 seconds
The Pain Master mutilates himself and takes a part of himself and throws it on an enemy hero dealing 100/200/300/400 magic damage and stuns him for 0.5 second. It also deals 50/100/150/200 True damage to the Pain Master.
Mana - 75/100/125/150
Cooldown - 15 seconds.
Fear the Pain
Fear an enemy hero and slow his movement speed by (10%/20%/30%/40%) and deals 25/50/75/100 magic damage for 3 seconds.
Mana - 100
Cooldown - 15 seconds.
Deals magic damage in 700 AOE equals to the number of HP missing of Pain Master multiply by (0.6/0.8/1.0). It also brings the Pain Master to 1 HP after the spell is casted (this isn't damage taken and it doesn't synergize with Share the Pain). You will also be invulnerable for 1 second after the spell is casted.
Chanelling - 2/1.75/1.5 second, before the damage is dealt.
Mana - 200
Cooldown - 100 seconds.
Why would you attack him ?
Because he has to ability to deal decent nuke, mini-stun and slow on your team. He will also be the reason why the enemy carry has so much survivality.
Why wouldn't you attack him ?
Because you will most likely fear the huge nuke that will come from his Agony spell.
What item would work great on him
Void Talisman - With good timing this item can help you land ultimate with huge amount of damage.
Elder Parasite - This is a really good item if you want to build Pain Master as a DPS hero. It will not only help you deal more damage but the Increase Damage Taken can be used to increase the damage you deal the enemy on which you have casted Share the Pain. So all the effect of Elder Parasite can be used positively (who ever tough the +20% damage taken could be usefull).
Behemoth Heart, Helmet of Black Legion - The more HP, the more damage your ultimate does.
Sacrificial Stone - This item bring you 4 great thing. First one is HP, second one is the reduction of the gold lost, third one is the reduction of the death time and fourth one it heals your ally when you die.
Barbed Armor - Wanna feel the pain even more ?
What are the combo and synergy of the hero spell
If you want to use Pain Master defensively or as a support hero you would max Share the Pain and Fear the Pain in first. Share the Pain would be used to protect your team carry and Fear the Pain to silence key hero on the enemy team.
If you want to use Pain Master offensively you would max Share the Pain and Mutilation in first. Share the Pain would be casted on an enemy and after you would use Mutilation on the enemy to deal not only the damage of Mutilation but also extra damage due to the fact that you lost HP from Mutilation.
The synergy of the ultimate is that Share the Pain (casted on ally) and Mutilation will get your HP lower just by casting spell and not being attack (because the other knows that your a big bomb when you use your ultimate). When you reach low HP, you will use your ultimate to do maximum of damage. It is most likely going to be a deathly blow, if it's not your in huge trouble, otherwise you might have got a Triple/Quad kill right there.
What hero can counter you effectively ?
Soul Reaper - This hero will make your ultimate be so hard to land since he can use his ultimate on you and kill you whenever your starting to be low HP.
Silence hero (Vindicator, Defiler, Dark Lady) - These can interrupt your ultimate with there silence
Mini-stun hero (Pharaoh, Tempest) - These hero stun can make your ultimate impossible to land.
Predator - Magic immunity will make him invulnerable to all your spell damage and with his passive ability that add extra damage according to your HP you will drop fast no mather how much HP you got.
What hero can be good match with you ?
Jereziah - With Void Talisman and his Ultimate (or Void Talisman), you will be sure to land your ultimate at the best moment.
Corrupted Disciple - This carry often build defensive item to be more effective, with your Share the Pain ability you can make him even harder to kill and more effective.
What hero can be good to play against ?
AOE nuker (Pyromancer, Valkyrie, etc.) - These hero will deal damage to you no mather if they want it !
What are the strong points of the concept ?
First,this is a hero that could use Void Talisman as a main item. This item is under-use and this hero could make a really good use of it.
Second, this is a hero that is versatile, it can be builded offensively or as a support hero.
Third, he can be countered by other hero and can be a good counter to other hero.