Which of the following words has a negative connotation?

Fresh

Rare

Soft

Tangled

I would say Tangled has a negative connotation

The word from that list with potential negative connotation is Tangled.

As a verb, it implies that something is being complicated or muddled probably with negative intentions. As a noun, it can be synonim for knot or for confusion. It can be used to imply that something is a mess, or a person is lost in a labyrinthic situation.

On the other hand, the other words have positive connotations: fresh can be applied to food that is in optimal condition for consumption or a breeze of fresh air that feels good.

Rare does not have a negative connotation. I. e. when you achieve a goal or do something that is not so common, rare implies that you beat the odds.