Is mockery considered apostasy, even if unintended or if the one who utters it is unaware of its ruling? And what is the ruling on marriage if apostasy is proven, especially considering previous instances of inappropriate jesting or swearing in anger?

One must beware of intrusive thoughts (waswas) regarding blasphemy or mockery. If a person repents with sincere repentance, Allah will accept their repentance. The questioner's marriage is valid. Describing someone as a terrorist is not mockery. The statement concerning the rain is an abominable utterance from which one must repent. A Muslim must guard their tongue and be careful in their speech, and abandon intrusive thoughts to avoid evil.