effort
hard
megachallenge
torfer
get into trouble
throw a wrench in
underchallenge
hard nut to crack
tough nut to crack
lightning in a bottle
make hard work of
take up
at a pinch
in a pinch
enodation
run for one's money
step to
chase
put a hurt on
defy
boil the ocean
wing and prayer
dare
doo-doo
unmess
square one's shoulders
pull off
queer someone's pitch
enmesh
line of attack
upseek
nodus
make an effort
square the circle
get out
hard-set
addressable
challengingly
gantlet
gauntlet
pain point
copout
hard put
draw a line in the sand
take the bull by the horns