What is the ruling on my saying: "Ugliness is apparent in his creation" about a person? Is that considered mockery of Allah's creation and does it lead to disbelief (kufr)? And does my saying this necessitate a ghusl, like one who embraces Islam?

This phrase does not imply mockery of God's creation, nor is it among the phrases that could lead to disbelief. Turn away from these whispers (waswas) and pay them no heed. Be cautious not to be lenient with whispers and to indulge in them, for their consequences are dire, and turning away from them is the best cure.