I'm about 8 years late and none of this info is particularly new, but in case anybody finds it useful assembled like this -
I'm going through the battle hall with the following set:
Garchomp
@Focus Sash
Ability: Sand Veil
EVs: 252 Atk / 4 Def / 252 Spe
Jolly Nature
-Outrage
-Earthquake
-Fire Fang
-Substitute
This set is easy to obtain ingame; even if you can't RNG, you can still easily get the two IVs that matter (atk / spe) with a combo of power items, everstone, and luck. Outrage can be tutored on if you don't want to chain breed and substitute is dumb in HGSS but you can cheat voltorb flip with a calculator, which may legitimately be faster than trading from dppt because the trading animation is so slow. you need a base gible in hgss from dppt if you're going to do it there, so remember to put a substitute tm (functionally buyable in dppt) on it if you do that.
mons to watch:
autoloses to the sash / ice shard weavile. has a solid 70% chance to lose to blizzard / ice shard glaceon that lives your outrage. clear dark + ice first to avoid both early on and pray you never see them.
quick claw:
dusclops (it lives outrage and qc ice punches you, actually infuriating)
bastiodon (it can freeze you with blizzard, but the probability of this all happening hovers at 1.4%)
lax incense / brightpowder + ice move:
jynx
froslass
piloswine
gastrodon
whiscash
pokemon that live an attack or are faster and have a chance to hax you:
lickilicky
poliwrath
machamp
slowbro
clefable
exploud
seadra
sharpedo (do not mash when doing water, or you will outrage and rough skin + ice fang will KO you due to its sash, can also freeze w/ ice fang)
hippowdon (via outrage self confuse from continued slack off)
yanmega (will live outrage and can flinch you to death with air slash if it endures the second outrage and has speed boost; only needs one speed boost at level 50 to outspeed you. needs to be outraged to guarantee KO at high levels)
abomasnow (level 50 fire fang has ~65% chance to KO factoring miss, even fire blast does not fix this without heavy investment)
literally every other ice type
scyther (is faster than you with sash and needs one crit for you to lose)
gengar (faster at level 50 and can hypnosis you or razor fang flinch, but will die if it misses either roll)
speedy or bulky evasion:
starmie (double team + brightpowder, will straight up 2HKO you at level 50 if it hits hydro pump then psychics or hydro pumps again)
crobat (double team, will flat out 2HKO you with at level 50 with BB if you're not lucky and BB recoil + outrage isn't enough damage)
espeon (brightpowder, but slower so you need to miss twice)
swampert (brightpowder + rest)
wailord (brightpowder + rest)
pokemon to play carefully against:
blastoise (use substitute to avoid losing to yawn, losing to hyper beam clones due to sleep turns stings)
uxie (use sub to avoid losing to yawn)
hypno (use sub to avoid losing to hypnosis)
scizor (use substitute and pray it does not use x-scissor you to the point of bp KO range; be careful of countersash + bp... alternatively, use flamethrower for bug, do not use flamethrower for steel because you need to actually KO levitate bronzong)
umbreon (use sub so it doesn't make you slowly KO yourself with confusion)
regigigas (safest way to beat this is substitute + praying for dizzy punch not to crit. earthquake a couple times til it dies)
raticate (be careful not to lose to focus band + endeavor + quick attack, aka the stupidest version of FEAR)
ursaring (be careful and use earthquake to not lose to focus band + rest + outrage confusion self hit)
best order is probably something like ice > dark > ghost > water > ground > normal > psychic > steel > bug > fight > flying > grass > rock > poison > (electric / dragon / fire).
a list of battle hall pokemon can be found in
this post.