Let the mage Get you low or Clear his hand (which ever happens first.
Drop Duskbreaker to clear the board, and start healing with light wells.
Mind Blast Priests (usually also bringing along a heal; can only burst you for 25 Damage, Fill your board with light wells and 1 duskbreaker, you win the fatigue fight if they don't concede before then. - Just keep in mind you take Fatigue damage AFTER Lightwell procs
vs Call to Arms + Knife Juggler - clear board ASAP (better if you get coin) - start dropping Light wells, put 1 down if you can but also save 1 in your hand for after you clear the board... he will empty his deck and hit fatigue extremely fast