Fluff/Tough

A lead-pipe cinch
Easy as pie, a gimme
Rolling off a log, shooting fish in a barrel, laughing all the way to the bank
Water from a duck’s back, candy from a baby, the eye of a needle, the skin of your teeth
Squeaking through, eking by, grinding it out
Harder than Chinese Algebra, a thicket of brambles
An Herculean task