Unfortunately, poor use of the Duel ability can lead to a quick loss. Thus, it is better to Duel dangerous but squishy supports, such as Zeus, Lina, or Pugna.
Recently, if you look at dotabuff, LC has been having a rough time lately, due to being counter-picked, although still picked 18th overall at the time of this writing. The recent popularity of certain heroes, such as Lina and Wyvern, have also hurt LC's win rate lately. It is also suicide to Duel against the recently-popular Leshrac, if he has his Pulse Nova and/or Edict active...
Insane Items for Legion Commander:
Silver Edge - a new item perfectly suited for the ganking LC; disabling your opponents' passives can be a massive benefit. Just make sure to attack once to get the bonus before you trigger Duel!
Desolator - This beautiful item has recently come down in price slightly, and is perfect for a 1v1 where nukes aren't involved. This item also allows ranged teammates to contribute significant damage to the Duel because of the armor reduction (Sniper, Viper, etc become VERY good teammates!)
Darn Useful Items for Legion Commander:
Blink Dagger - a useful item on any melee initiator, LC is no exception. Just don't blink too far ahead of your team, or you might be Duelling your enemies 1v5.
Black King Bar - it's very frustrating as LC to never be able to Duel because of Silences or Stuns. Opponents like Drow or Death Prophet often require LC to have a BKB to have much chance of initiating.
Pipe of Insight - Believe it or not, this is a Dueling item. Not solo-dueling of course, but it helps against heavy-nuke teams where opponents can't easily nuke LC down once he begins a Duel. LC can usually afford a support item like Pipe because of her decent farming ability.
Assault Cuirass - like the Desolator, this item's armor reduction gives great benefit, but it also gives something LC lacks - attack speed. As you gain bonus damage, gaining attack speed gives more and more benefit to your DPS.
Team Building Suggestions
Despite LC's versatility, certain heroes really help her to shine (or suck, if on the other team):
- Vengeful Spirit: More armor reduction and boosted attack damage? And a Swap to get her out of a losing Duel? Yes, please!
- Sniper: Long-range, reliable damage to help win duels is GREAT.
- Enigma / Tidehunter / Dark Seer / Winter Wyvern / Magnus: All of their ultimates make great distractions to help win Duels.
- Dazzle / Omni: Well-timed Repels or Graves help win (or lose) clutch Duels.
- Lion / Lina / Zeus / Nature's Prophet / Ancient Apparition: Why win a Duel fairly if your teammate can nuke heavily, possibly with a Global range?