For the golem I like the 3 armor, it is clearly a golem made of bones grafted together in an unnatural and fortified way, rather than a resurrected skeleton.
However, so many things have piercing these days. I think that 13 health is too little for 18 mana, the skeleton knight seems the better choice with same amount of attack dice and a defense. I vote for 16-18 health with the 3 armor.
Edit: Okay, I overlooked his rot chance, that makes him a lot stronger. With more health you would probably have to make the rot chance less, not sure. You could also consider the lumbering trait or something to that effect (i think slow would be too much), since other golem-like creatures are hindered in their move.