mountain
task
praemunire
crux
pain point
brainteaser
rub
bad boy
have a mountain to climb
three-pipe problem
tough nut to crack
mountain to climb
hard nut to crack
challenge
stumper
stumblingblock
mission impossible
Matterhorn
poser
snag
lightning in a bottle
nodus
doo-doo
superchallenge
glove
situation
dilemma
queer someone's pitch
difficulty level
job
shit
daunting
bear
skittish
pull teeth
tough
problem
unsimpable
hard going
ambitious
hard time
rush job
pig
trouble
mean
chore
torfer
over the river and through the woods
hard yards
tall order
eke out
overchallenge
hard-set
trickily
throw down the gauntlet
enmesh
large order
uphill
bring off
difficultate
multichallenge
run for one's money
proposition
enigma
killer
riddle
brain-teaser
conundrum
challengingly
problematic
challengeful
tightrope
hard times
challengee
try as one may
perplexed
hardpressed
dys-
hard
monkey wrench
complicated
boil the ocean
laboring oar
recalcitrant
snorter
underchallenge
make hard work of
long row to hoe
grind
wrestle
arduous
bitch
square the circle
counterdifficulty
between a rock and a hard place
hack