When these things are in the yard, do they count as creatures, instants or both?

They are always only creatures, unless they are on the pile as sorcery/instant then they are that and only that (you cant use a counter against creature to block an adventure, and you cant fetch the card from anywhere by looking for instant/sorcery)

Standard Black players are saddened by the loss of Vraska's Contempt. This may take its place. This costs 1cmc less and has a creature attached to it, but the "destroy" instead of "exile" is a serious downgrade. Life loss instead of life gain is a less serious downgrade, but still renders this an inferior card. That being said, it's a Zombie which is always a relevant type and a Knight which is a relevant type in this set. The potential reusability is a nice bonus. Although, that takes away from Black's typical reanimation plan, especially where Zombies are concerned.