Comrades and Saboteurs
This guide is primarily pertaining to the combos and counters that Tresdin's unique ultimate Duel creates. Its not a full hero guide yet and its also my first guide, so it won't be all fancy for a while.
Legion Commander needs three things for a successful Duel:
-Getting right up to the enemy to cast Duel
-Protection from dishonorable foes that would interfere with the Duel
-Help from [strikethrough]dishonorable[/strikethrough] allies to ensure victory!
Some of these Tresdin can do himself (eg. blink dagger or Lothars can get you up to the enemy), but if you're teammates can do it for you so much the better. Friends are categorized based on how great of a general they make you.
ALEXANDER THE GREAT
These heroes make Legion Commander win absolutely every Duel by giving her everything she needs and more.
In Dota 2, Tresdin will not ride a horse, she will be carried on the back of a double-headed dragon. Jakiro gives you everything and the kitchen sink: A slow (Dual Breath) and a stun (Ice Path) to let you catch the foe, two attack speed slows (Dual Breath, Liquid Fire) to prevent the enemy from doing too much damage to you, and incredible ultimate synergy in the form of Macropyre.
Macropyre deals massive damage (up to 1575 at lvl 3 w/ Aghanim's before resistance) over the duration, but the enemy can always just walk away...unless they are pinned by a Duel. Then they have to stand in the flames for almost the entire duration. Also, any pesky non-duelled enemies are effectively zoned out by the flames.
If both of you can land your ultimates, you can take down an enemy hero every minute (Duel cd is 50s, Macropyre is 60s).
There is only one thing the Oracle sees for Tresdin: VICTORY!!!. You see, Nerif's lore left out the bit where he falls head-over-heels in love with Tresdin and devotes his life to impressing her.
He can purge-slow an enemy for up to three seconds with Fortunes End. He can heal you with Purifying Flames. He is a walking, talking Heaven's Halberd on steroids with an up to 6 second disarm+50% physical damage enhancer (Fates Edict). However, even after all this Tresdin still wouldn't give Nerif the time of day ("Why do you need me to give you the time? Aren't you an Oracle?"), so he decided to make the best, bar none, ultimate combo in the game in the form of False Promise.
False Promise gives 7/8/9 seconds of Slark Ultimate (invisibility that won't be broken even if you attack or use abilities). So LC can just walk up to her target and have an entirely one sided, surprise Duel. "But what if the enemy has detection or AOE?" Never fear, False Promise also makes you IMMORTAL! Well, not quite immortal (hence the "False" bit), but it does make sure you won't die while Dueling which lets you finish up or at lest not feed. You see, False Promise delays damage and heal until the end of the duration so Tresdin could potentially 1v5 initiate with a Duel and win...the Duel. She'll still probably die when the False Promise duration ends.
You know what, I take back the thing about Tresdin steed being a Jakiro. She will ride around on Nerif's shoulders.
Witch Doctor has a pretty good stun (Paralyzing Cask), a great damage enhancer (Maledict), and a nice AOE heal (Voodoo Restoration) that keeps you alive during and after the Duel. He also can set up a murder turret to mow down the person your Dueling and any enemies in the area. A lvl3+Aghs Death Ward will deal over 3000 damage to each target over a lvl3 Duel duration. Nothing will survive that.
These heroes don't let you win Duels when the opponent is full HP and the entire enemy team is there and its just you two, but they make you hella powerful particularly in the early game.
As a fellow general (who also got expelled from his home world in the midst of battle), Dark Seer knows what Legion Commander needs. But since she is still a round-head, he's not going to give her everything. Surge and Vacuum make it cake to get in range of an enemy. Ion Shells on Tresdin and Dark Seer will melt most heroes in the early to mid game. Wall is also good at zoning other enemies out but needs to be well placed. He will even solo lane for you while you jungle! Dark Seer almost made the Alexander class.
Slows enemies movement and attack speed around him, gives you magic immunity, heals you while damaging your foes, and can save your *** if a Duel goes to hell. He's here primarily because Repel can let you skip or delay BKB, letting you snowball faster.
Has a slow and a pin, while being a mana fountain that lets you spam abilities in the jungle and a gank. Meanwhile, you pin for her ulti which deals significant damage while cutting MS and AS. This means more successful Duels and zones out enemies well.
Holds the enemy in place (Nightmare), nice nuke (Brain Sap), and makes enemy autoattacks do nothing (Enfeeble). Fiend's Grip can also feed Duel wins to Tresdin (particularly early game), although the CD is a bit too long to devote it to givng LC Duel wins.
Can help you get in position with Cyclone and Ice Wall, has a stun+disarm, and has a ton of AOE skillshot nukes that you set up nicely for.
You work well with these heroes, but they won't let you take Russia.
Good initiator that can slow (Battle Hunger) and pin people for you to get into position (Berserker's Call). Culling Blade can ensure victory in a close duel or cut through Shallow Grave and Borrowed Time.
Slow/stun, heal, armor buff/debuff. Most importantly, Shallow Grave prevents you from losing Duels.
Powerful nuker with a 4-second disarm (Laser). Can send an army of robots at your conveniently pinned foe while zoning out the enemy team.
Armor reduction aura, skill shot nukes. For extra pwnage, can phase boot onto the Duel opponent and cast ultimate for about 2000 damage.
Mana fountain with an unreliable stun (Mana Drain) and powerful nuke. Can call you in for a gank with his ulti, and effectively disarm in an AOE.
You just set up his combo so well. Can get you in range with x-marks the spot.
Your pin sets up well for her ultimate and nukes. The silence can be helpful to prevent an escape and prevent harassment.
These are the knaves that just ruin your day by preventing successful duels, even if you have magic immunity.
There's a reason the lore has a Tresdin v Abbadon duel which doesn't go anywhere (except another plane of existence). Its almost impossible to win a Duel against the Lord of Avernus, so don't even try. Forget the massive advantage Frostmourne gives him in a slugfest, you can never kill him because of his gamebreaking ultimate. Borrowed Time will trigger through a Doom when he goes below 400 health and it can last longer than your ultimate. Not to mention you're own ability is making you hit and heal him.
If Tresdin and the Oracle break-up, he won't take it well. False Promise can prevent you from winning Duels too because the enemy can't die. He can also pop False Promise and run if you try to initiate on him because it only has a 20 second cool down. If you aren't magic immune, he can Fates Edict you and you are almost definitely going to lose that fight.
Shallow Grave prevents you from winning Duels. Either initiate on him before he can cast it, or have an Axe on your team.
He'll just disappear you're opponent for 4 seconds, meaning you won't every be able to finish a duel. If he sees you initiating on him, he can disappear you and run.
Nai'x eats melee strength heroes for breakfast, lunch, dinner, supper, brunch (you get the point). You won't be able to do more damage than he lifegains usually. He can also go magic immune for almost the entire duration of the duel if he knows you are coming.
His ultimate melts your armor while damaging and goes through magic immunity. He can steal all your damage through magic immunity. If you aren't magic immune, Unstable Current will slow your AS by 100, so you'll barely even hit him. He's also fairly tanky. If you can surprise initiate you can still win. If you have an ally like Jakiro around victory is also quite likely.
While she can't prevent you from winning every time if her ulti is up you will probably die. The ultimate won't stop if you duel her and deals a TON of physical damage, you can't run, and she is tanky enough to hold out for a while if you are Dueling her. If you surprise her, she's food.
Can be cast on a Duel opponent to make them invulnerable for 2.5 seconds. Two casts would completely nullify your Duel.
These opponents will mess you up if you don't have magic immunity. If you make a stupid and don't have BKB or Omni, then prepare to lose. I'll list the Duel opponents that will mess you up, and the good news is there aren't many. The bad news is that there are a lot of enemies that can ruin your Duels against someone else. The thing about Tresdin is that (if she isn't magic immune) the heroes that have great synergy with her counter her very well, since Duel pins and Dooms LC too! Remember this when picking and banning in Captains mode.
Tiny isn't quite as bad as the above, but he is a tank with high DPS and low AS that can mess up your initiation with a Toss and/or (if you aren't Magic Immune) a stun. Craggy Exterior will mess you up if you aren't magic immune.
Tank with a massive bash. Can initiate on you well and can run away with Charge of Darkness.
Special Mention: RUBICK
Rubick is food for you if you Duel him, but the reverse is true if you Duel someone else and he is there while you are not magic immune. He can reduce your attack damage and disable you for 4 seconds. If you survive, he'll cast the Duel he just stole on you which will let them finish you off.
One great thing about Duel is that it prevents escapes and can turn formidable opponents into impotent trainees. Weaver? Clinkz? Storm Spirit? They may be cowards, but at least they have the honor to respond to a Duel. There are several heroes which you counter particularly well:
The bane of pubs is little more than a cat with a knife before you. Not only is he a glass cannon that relies on invisibility, blink strike, and smoke to survive, the "cannon" bit relies on being able to backstab foes. Guess what? Duel forces him to stand in front of you.
QUEEN OF PAIN
She is both an Escape and a Nuker. You easily bring too much pain even for her.
Slark is usually hard to kill. He can purge debuffs, pounce away, and can go invisible with his ultimate. If you lose sight of him for a second he will get a massive move speed bonus (to max speed by midgame) and regen, so he will be gone and then return with full health a few seconds later. However, he can't run when Dueled. If Duel's Doom has the same mechanics as Doom's Doom, then Slark won't be able to purge it with Dark Pact. The Legion will fest on fish tonight.
This may be controversial but I think Tresdin can own Mortred, even if the latter is fully fed. PA relies on Blur to survive (disabled by Duel), HoD or Satanic to survive (most passive Lifesteal disabled by Duel), and Blink Strike to escape (also disabled by Duel). Most importantly, her primary damage ability Coup de Grace is also disabled by Duel. The Legion does not tolerate assassins.
ROFL COUNTER: DOOM
You can't Doom me, I Doom you! Since you are built to fight while Doomed, Doom can't counter you well.