master key
square the circle
problem
trouble
entangled
enmesh
boil the ocean
hash out
rise to the occasion
rise to the challenge
hard yards
challenge
enodation
counseling
toughness
ingenuity
formidability
resource
hard-set
diagnostic
lightning in a bottle
ministration
killer
succour
hack
relief
succor
megachallenge
crack
superchallenge
task
rough sledding
pull teeth
mission impossible
hard time
snorter
rigour
bring off
spinous
navigate
over the river and through the woods
high-hanging fruit
pressure point
handful
waymaking
challengingly
marathon
finagle
hard nut to crack
hard going
unwieldy
solvability
torrid
overchallenge
endurance contest
tough nut to crack
another string to one's bow
solution
counterdifficulty
uphill
mean
voodoo
unmanageable
uncontrollable
kink
dys-
heavy lifting
go at
convenient
laborious
tool
pain point
bitch
skittish
pull through
an old dog for a hard road
Rube Goldberg machine
challengeful
siege
escape fire
puzzlery
torfer
catch a cold
dare
defy
conquest
leg up
put a hurt on
do-or-die
imagination
resourcefulness
three-pipe problem
queer someone's pitch
kludge
doable
feasibleness
hard hit
come to grips