difficult
hard
arduous
a hundred and ten percent
hard time
rough sledding
pull off
hardpressed
difficulty
pull teeth
lightning in a bottle
power
ruggedness
hardness
Matterhorn
difficultness
daunting
conquest
exert
mission impossible
struggler
laborious
gutless
hard-won
underchallenge
tryingness
challenge
pain point
back
resource
bring off
cumbersome
strained
punishing
un-get-at-able
toilsome
uphill
backbreaking
stubbornness
grueling
obstinacy
un-come-at-able
operose
mulishness
heavy
difficulty level
ungetatable
obstinance
gruelling
chase
arduousness
underexplored
strenuousness
sweat out
venture
pedgill
complicated
have a mountain to climb
gotcha
inaccessible
try as one may
winning
challengingly
an old dog for a hard road
unaccessible
undemandingness
semiskilled
break a sweat
mountain
inefficient
demanding
hit
ineffective
steely-nerved
ungainly
plucky
elusiveness
wrestle
challenging
hard as nails
purchase
pushability
come at
resourcefulness
labour
give it some welly
eke out
rise
situation
strivingly
nonability