Mulligans
General Mulligans
Your number one preference is Barnes. Onyx Bishop is also a keeper if you have Barnes. (decreases the likelihood of getting a vanilla Barnes guest).
Failing that, you will want to keep any of the other four cards and mulligan all others (especially the Legends).
You'll want to wait to get a critter out that you'll want to resurrect so resist the urge to cast any copied critters you get from your copy spells.
Aggro Mulligans
Remember, Barnes always. These others to hopefully survive the initial weenie onslaught. Maybe also keep Priest of the Feast to get your spell healing going asap.Midrange Mulligans
Try to eliminate early threats. Tuck the big threats you like and destroy the ones you don't.
Resurrect Priest deck without Injured Blademaster. Slower, but Barnes will likely fetch a game changer.