I think these are the ones I find the worst:
Cerberus (WAY too expensive for a guard dog without intercept)
Earth elemental in the current meta. (could change in the future with a new mage)
Goblin bomber (I don't get why he is not level 1 and 4-5 mana instead of 8 )
Infernian scourger (Other people like him, but I think he sucks. Art is cool though)
Makunda
Moonglow Fairy
Psylock
Selesius (could also change with the meta if more flyers get used)
Tarok (Same as selesius)
I generally agree, but I often put Tarok in Beastmaster books because the BM has relatively few ways to deal with flyers (e.g. aside from attack spells).
Other less-than-stellar creatures (imho):
[mwcard=MWSTX1CKC09]Giant Wolf Spider[/mwcard] (cool theme, but way too costly in terms of mana, sbp and the effort needed to activate the Stuck gimmick)
[mwcard=MWSTX1CKC03]Galador, Protector of Straywood[/mwcard] (not objectively bad, but high sbp cost when you could just have Cervere or Bridge Troll or something; might see more use if Priest/Priestess/Paladin become more viable - e.g. if creatures with Lightning +X see more play)
[mwcard=MWSTX2FFC12]Talos[/mwcard] (seems OK if you could hard-cast him, but when you put in the ridiculous work to get him in play (which I've done several times for giggles), he just doesn't do enough to warrant the ridiculous work needed to get him in play)
[mwcard=MW1C40]Whirling Spirit[/mwcard] (upkeep for a creature that dies vs Wizard; might get better now that Wizard sees less play AND since Wizard must be trained in Air... and seems like it might be good in Domination, where board control and Push effects are very important)
[mwcard=DNC18]Togorah, Forest Sentinel[/mwcard] (despite being Vigilant, he doesn't counterstrike, and a Guardian Angel is almost always a better option)
Actaully, pretty much any of the 20+ mana creatures except for Adramelech (e.g. all the big legendary angels, Togorah, Earth Elemental, etc)
As for the topic at hand, I think Sardonyx would be OK if he only cost you 1 life per turn, and if his zone attack was 3 attack dice and dealt Rot on a 5+. As it stands, you'd generally rather have him using one of his [mwcard=FWQ04]Galvitar[/mwcard]-like melee attacks and sticking close to his opponent for his Poisoned Blood effect. Actually, I rarely find the Poisoned Blood thing useful as I generally have Deathlock running anyway. But maybe that's why Sardonyx usually kills my mage before the opponent: I'm too busy doing other things rather than supporting Sardonyx with Restrain effects (on his targets), walls, etc.