Alright so first, rulelist. The other two answers are correct on this. I'm just going to copy paste it from one of my old answers which can be found [here]
>Moves: Dragon Rage, Sonic Boom, Swagger, all Evasion and OHKO moves (as well as any strategy which forces endless battles).
Pokemon: Gligar, Misdreavus, Meditite, Murkrow, Scyther, Sneasal, Swirlix, Tangela and Yanma
Eviolite - Probably by far the most common item. Due to the fact that all LC Pokemon are in their basic stage, Eviolite becomes a very common item to buff their defensive stats. LC walls like Vullaby, Foongus and Porygon will use it as well as a large majority of tanks + bulky attackers.
Berry Juice - a popular item choice, normally for Sturdy users. Berry Juice, in LC, will almost always restore a Pokemon back to full health, which works nicely with Sturdy, giving the Pokemon 2 sturdy shots, provided Rocks aren't up or something.
Choice Scarf - in every tier, Scarf is a common item, and there's no except ion LC (Though, the emphasis on Choice items is much lower, so the frequency still won't be particularly high). Scarf is used on revenge killers
Life Orb- a common option for more frail attackers, giving them a much needed boost.
In reference to Trapinchator's advice;
>Get a level 5 Pokemon will 19 hp(not sure how you get it) and give it the life orb. So when you use an attack you will lose 1hp.
I would say, DO NOT use that as an important requirement to fulfill. This is because you need quite a low HP stat in order for that to occur (Here's a comparison: Shuckle, one of the Pokemon with the lowest HPs at base 20, has a HP stat of 18 at level 5 while uninvested. Common attackers like Pawniard have 21 without investment).
However, it is advisable to not use HPs that are divisible by 10 on Pokemon utilising Life Orb.
Other somewhat usable items - Focus Sash, other Choice items.
>Also 180 EVs on a level 5 Pokemon is equivalent to 252 EVs on a level 100 Pokemon(just pointing that out there)
^ From Trapinchator. Incorrect
The amount of EVs you require for an LC Pokemon to reach the maximum the stat can go to will vary depending on the stat. 236 is the absolute maximum amount of EVs you will need, but other times you may need 228 or even something like 196.
Smogon has done the calculations for them [here;]
>Base Stat Ending / EVs required for stat gain
xx0 / 36 /116 / 196 EVs
xx1 / 28 / 108 / 188 EVs
xx2 / 20 / 100 / 180 EVs
xx3 / 12 / 92 / 172 / 252 EVs
xx4 / 4 / 84 / 164 / 244 EVs
xx5 / 76 / 156 / 236 EVs
xx6 / 68 / 148 / 228 EVs
xx7 / 60 / 140 / 220 EVs
xx8 / 52 / 132 / 212 EVs
xx9 / 44 / 124 / 204 EVs
So, to give an example if I had a Pokemon with a HP stat of 88, I would need 212 EVs to maximise that stat.
Threats to think about while teambuilding
This is one of the three S-rank threats in LC.
Fletchling has the ability to set up SD, and with it's ability Gale Wings, it can ignore speed and fire off Acrobatics, decimating unprepared teams. It is very important that you have a decent check to Fletchling while teambuilding. Generally, Pokemon which can tank +2 Acrobatics and respond with a move that OHKOs are good checks and so on.
Pawniard, the second S-Rank in LC. Again like Fletchling, it can sweep through unprepared teams given the chance, and is a pretty good Pokemon the clean the opponent up with.
With the ability Defiant, as well as access to STAB Knock Off, Pawniard has the ability to 2HKO a large portion of the tier. Iron Head plonks any Fairy Types and Sucker Punch provides reliable STAB. Scarf Pawniard is also a relatively popular set.
The last of the S-Ranks, Mienfoo.
Mienfoo has the ability to go down both a very offensively based route, and a more tank based route. Reckless and Regenerator are two very useful abilities, with Reckless pairing very well with High Jump Kick and Regenerator being a very useful ability on more bulky sets, and working well with U-turn. Again, Mienfoo can potentially sweep unprepared teams.
Those three are by far the main threats.
However some other good threats to consider using/countering are: Archen, Chinchou, Drilbur, Magnemite, Abra, Timburr etc.
Those are all A-ranked LC Pokemon.