What is the ruling on someone who mentions Allah playfully, such as saying "In the name of Allah, Most Gracious, Most Merciful; I seek refuge in Allah" in mockery? And is it considered mockery of religion and the laws of slaughtering if one acts out slaughtering their brother as if he were a sheep?

The prohibition against the questioner joking about religion does not indicate his disbelief or falling into disbelief or his mockery of religion, just as his jesting with his brother does not indicate mockery of the rituals of Allah. Therefore, he should turn away from obsessive thoughts and fill his time with acts of obedience, occupying himself away from satanic thoughts.