dare
defy
counterchallenge
test
provocate
appeal
challengeful
glove
challenge
dys-
superchallenge
challengee
mountain to climb
heckle
challengeable
daunting
overchallenge
throw down the gauntlet
run for one's money
megachallenge
mountain
go up against
lightning in a bottle
stumblingblock
toughness
underchallenge
formidability
rise
rigour
hard yards
nodus
difficulty level
rush job
brick wall
over the river and through the woods
killer
doo-doo
testing
rough
challenging
trouble
have a mountain to climb
skittish
problem
double dare
multichallenge
tall
push
nonability
labor