Hawlucha has excellent physical attack and became one of the most popular Pokémons....I think.
Eerm... its Attack isn't that great compared to other physical attackers at base 92, which requires a Swords Dance boost. But it has excellent Speed, at base 118, which combined with Unburden boost, allows it to outspeed many Pokémon.
Here's the OU set of Hawlucha brought from Smogon:
Gems are illegal in Gen VI.Hawlucha only really has one thing going for it, which is Speed, as otherwise, there's usually going to be another Fighting-type or Flying-type that can do what Hawlucha does, but better.
+ Base 118 Speed is fast on its own, but combined with Unburden, it's able to outspeed every unboosted Pokemon in OU, giving you the "edge" every turn.
+ It's able to learn a surprising array of moves including High Jump Kick, Acrobatics, Fire/Thunder Punch, Drain Punch, U-Turn and Low Kick for specific threats.
+ The Swords Dance + Unburden combo destroys teams that aren't prepared for it.
- Base 92 Attack is subpar, by OU and Fighting-type standards, so it can't really do much on its own.
- Two of your moves are used up by Swords Dance and Substitute (normally), leaving not much room for coverage moves.
- Doublade, Mega Slowbro and Unaware Clefable wall it, even at +2.
- Priority moves are a problem for Hawlucha, such as from Mega Pinsir and Talonflame.
- 78 / 75 / 63 bulk is poor too, meaning it's usually OHKO'd by super-effective moves.
- Doesn't learn Belly Drum. I think Slurpuff if better at the whole Unburden ordeal.
Limber: This Pokemon cannot be paralysed. This ability is nice considering that paralysis will shut down Hawlucha, but it is often overshadowed by its next ability.
Unburden: Once your held item is consumed, your Speed doubles. Like I said, this allows Hawlucha to outspeed every single Pokemon in OU, so it's worth using alongside a Gem or a Sitrus Berry.
Mold Breaker: Moves can be used regardless of the foe's abilities. Hawlucha doesn't have too much use for this ability, as it doesn't not prevent it from hitting Ghosts or whatever.
High Jump Kick
Item: Sitrus Berry / Fighting Gem / Flying Gem
EV's: 12 HP, 244 Atk, 252 Spe (if Sitrus Berry is being used OR) 252 Atk, 252 Spe, 4 HP (if a gem is being used).
So you have to use up your item before you get the Unburden boost, right? So why not use an Attack, get the boost from the gem, then get the Unburden boost?
Substitute would probably have to be used first, followed by SD or an attacking move, if you are using a gem, followed by SD. Just be careful about the 90% accuracy of HJK: if you miss, you lose half of your HP.
If only Hawlucha got Fake Out.
Hawlucha having excellent speed combined with Unburden boost, it can even outspeed a Weavile and a Rapidash and any Pokémon who are known to be the fastest.