Deck can have very odd and unintuitive mulligans such as
KEEP vs:
glugg/azshara – druid, mage, dh (also hunter for glugg)
devourer – dh, paly, shaman
fool/multicaster – priest, shaman, mage

notable DONT KEEP vs:
2+ removal vs priest
3+ spells vs mage (in case of big spell)
bolner/brann – everything except quest priest
denathrius – shaman (u win on board most times anyways so just dont get it sniped)