Duriel by Demolij

Duriel is a melee assassin with a ton of durability. Masochism lets him absorb a crazy amount of burst damage, and is somewhat similar to simply having 50 armor at all times. It isn't perfect by any means though, since all it means is lethal damage will kill him a few seconds later, and with enough damage enemies could potentially just nuke through you. On the bright side, the rest of your kit has a lot of synergy with how much damage you've taken, and with effective healers and good dps he can be a strong frontline. But most of all, his raw damage output is absurd due to Masochism, letting him hit for undeniably the highest in the game under specific circumstances. Duriel fits in best where he can absorb damage without being the only damage absorber, and can do great as a melee dps.

Duriel has limited mobility tools, and doesn't have any ranged attacks or activated mobility tools, instead all his power is centered around him. This might sound like he's not very mobile and needs a way to keep up with enemies, which is where Slither comes in. It's not very good out of combat or of much use for kiting, but chasing enemies down with mounted speed is extremely powerful, especially when you don't need to land basic attacks or anything for it to work. It can't be used as an escape but your slightly amplified movespeed will help with that. He is actually very good at dealing with hyper-mobile enemies as well due to his other abilities.

If you are getting hit hard you can simply hit them with Flay in retaliation for a short breather and some decent damage, although you should be careful with using it since it prevents you from landing a follow-up strike. Maggots are great because they give you some Pain to boost your damage, but even better it will infest enemies causing them to take some damage to dissuade enemies from attacking. Pain Monger is the ultimate counter to mobility, causing enemies to take a decent amount of DoT whenever they move even if they move away, and a greatly increased amount whenever they move quickly. It's unlikely to outright destroy someone if they're just walking normally especially due to the passive slow, but against movement abilities it will chunk really hard. I don't want it to be too hard a counter against global heroes though, so it has no effect on specific abilities like The Hunt or Falstad/Auriel flights. It does trigger on Genji dash though. Just wanted to bring that up.

Suffering is pretty simple, it temporarily gives you all your health back. It's great for dealing with burst if you're not stunned, but even against heavy sustained damage it can still buy time enough for your teammates to arrive or for you to restore health. The damage dealt is enough to grant you a nice chunk of Pain as well. Bloodletting on the other hand is a deadly offensive tool that marks an enemy you don't like so you can chase them around while healing yourself up, and after a while you will chunk them for a bunch of damage as long as you stuck to them long enough. The trail they leave behind is decently large and can make it hard for them to flee, especially when you've got Pain Monger damaging them the whole time. Both are amazing dueling tools with slightly different methods of application.

When it comes to talent options, a lot of his numbers are untested but here are some suggestions. Level 1 is an important tier that works with how your Pain is handled, giving you the option of flat-out reducing the damage you take and deal for safer play, delaying the damage you take so you can attack at will, and increasing the efficiency of damage taken. From there you can pick talents to greatly impact the reliability of your skills, and increase your damage dealt when possible. What's important, however, is that at level 13 you get 3 powerful offensive options to spike your damage, and at 16 you get some of your only real defensive options you can have.