This is not a sentence.
There is a noun "mind", which is modified by an adjective "creative" and a relative clause "that want to develop in every possible way". There is no main verb.
Now in this phrase, the relative clause is headed by a pronoun "that", and in this case, the relative pronoun is standing for "mind", a singular noun. So the verb in the relative clause (want) needs to agree, and should have the form "wants".
A dog that has a bone is a happy animal.
Singular dog, so third person singular "has", also the main verb is "is"
The birds that fly over my house come from Africa.
Plural "birds", the verb "fly" in the relative clause and the main verb "come" are both third person plural.
A dog that I own is happy.
The relative clause "that I own" has its own subject, and the pronoun "that" is the object of the relative clause. The verb "own" is first person singular, but the main verb "is" is third person singular.