What are attributes necessary of a champion to excel in 1v2 lanes?

Recently in the LCS, I've seen many teams send a solo laner to deal with the duo of the AD Carry and the Support.

What are necessary attributes of a champion to do well in this environment? How can I do well (or at least, not do poorly) in this lane? What champions are able to survive and thrive against such a duo?

You're thinking of it wrong. You must first ask yourself : why should I be solo bot against an adc + supp?

The answer shouldn't be: "because I can sustain damage and kill the support".

When you choose to go into a duo bot lane alone, you put yourself in a disadvantageous position from the start. However, the reason you would do this is so that your normal duo partners will rock the top lane, get a fast tower, etc.

What is your role as a solo bot then? One word: farm. Don't dream awake, you won't be gently last hitting in the middle of your lane, getting creeps, hitting a champion. Should you play against me (as support), I will assure that you have no choice but to hug your tower until its down. And you won't be able to do otherwise because if you don't, we will just burst you down 2v1.

Now that I have ruled this out, some advices:

• Get a champion with good sustain (lot of life, regen, heal, etc)
• Get a champion that is good/fast farmer: you will need to be able to clear your waves easily and under tower. AoE spells will help.
• Having some crowd control can be good: you can punish a champion that wants to come too close to your tower

Range or melee? I think that in this situation, it won't matter very much. Range may help you get some fresh air, by attacking the enemy duo more often. But if both are ranged too, that may be difficult. Melee champions will have the advantage of being able to farm correctly under the pressure of the lane.

In your situation, a good pusher/bruiser would be the best choice. Which one strongly depends on the enemy duo team.

Zed seems to work surprisingly well. He can last-hit with Q on a fairly short cooldown, doesn't need to worry about sustaining mana, and after a couple levels can waveclear at a distance with W-E.

Don't get me wrong, you're still going to lose the lane, you'll just hopefully lose it slower than your opponent loses their single lane.

Start Red pot, health potions. You probably don't need a ward for lane unless they have a Thresh, Blitz, or other long range dangerous CC, in which case you might want one for near bush.

Your goal here is to sustain in lane as long as possible, collecting last hits when you can, and avoiding death and damage onto your tower. Don't waste time harassing champions, unless you can do it without taking any damage, or missing any minions.

Once your team takes a tower, your job is done. Switch lanes back with the duo pair, and let them push their gold advantage, while you push yours in the top.

Edit: With the recent price changes to red pot (3.6 patch), taking it will limit your sustainability down to 3 health potions. This is probably too few. Cloth Armour 5 pots is probably a better strategy, although it will cut down on your ability to harass and accomplish much with a surprise jungle/mid gank.

Wow no one said it yet and I'm sort of surprised, but I have actually done this a few times in early ranked S2, whenever we had an alistar/janna/eve/twitch or roaming type character.

Cho'Gath is the champion you are looking for. You need to be fairly skilled with him, however, because if you get poked down and forced to B early, you'll be behind and will never recover.

But the basic idea is that you save your mana for Ruptures, level up your Vorpal Spikes first, and focus on getting every last hit possible. (that is your sustain). I would start 9 pots 2 wards, or cloth 5. If you can survive the first 7 minutes, you should be level 6 by the time they hit level 4. At that point, it's an easy Feral Scream > Rupture > AA > Feast combo to take down either the ADC or the support, preferably the ADC.

I would go 9/21/0 masteries, and I would go mPen marks, armor yellows, scaling MR blues and MS quints.

Core build would be something like RoA, FH, Nashors Tooth.

Renekton is a really good 1v2 champ, with slice and dice you can be in their middle and out before they know it, while still doing a little bit of damage. He is a melee champ though, which will make your job hard against the ranged adc.
Warwick is similar, as soon as you have your ulti, you can jump in and lifesteal the hell out of them, but he is not that good in late game team fights.
Rumble has a really good ranged poke and a decent amount of sustainability, he is also mainly AP, which is something most adcs will not rune against.
Jax is the ultimate dueler, and can manage a 1v2 lane, because of his ability to jump in and stun both, it's really good if you get the occasional gank from your jungler. His jump can also be targeted on wards and minions, so you can use it for escapes as well.
Yi has a massive heal, and a really long range poke, but it puts you right in their middle with no way to get out except run.
ZAC can sustain pretty good as well, and has a really good escape tool. His passive is there so you don't die even if you make a mistake.

I wouldn't dare to suggest builds for most of these, because I don't play them, but I do play Jax, ZAC and Warwick occasionally. Jax really benefits from a mixed ap/ad build with life steal and spell vamp. Warwick is good with attack speed and life steal. I haven't found my perfect build for ZAC yet, but his 'w' does %max hp damage, and scales with ap.

Well, this really depends on what kind of setup this is. If the opposing champions have a hard CC, spell shield is a must. Champions with a spell shield are Morgana, Nocturne and Sivir. From this list, only Morgana would provide sustain with her passive.You could pick Gangplank for similar reasons - he can clear CCs and has a ranged poke. Tho he is a melee, so it would not be too safe.

If the opposing champions does not have any hard, non-skillshot cc, then options are wider. Most of solo-top pokers come in play here. The key is mobility and/or sustain. Teemo would do good, as well as AP Janna, Lee Sin, Yorick and Mordekaiser. Some people suggest Galio, but I have not played with the champion. Another interesting choice would be Heimerdinger, but thats tricky and mistakes are punished severely.

You have to understand, that playing solo bot will not put you in a position where you can harass much, it is a defensive position. To pull it off, good gank coordination and warding is needed. Also, a good bet is that a lane will be swapped, making it a solo.

TL/DR:

I don't suggest it, but if it is an absolute must, Morgana would be my best pick because of Spell shield, CC and sustain. Alternatively, use Gangplank for sustain, poke, buffs and global presence.