I. As a king of Kantipur, Pratap Malla built many artistic architectural structures in Kathmandu.

Here are the completed sentences based on the provided text:

I. As a king of Kantipur, Pratap Malla built many artistic architectural structures in Kathmandu.
II. Pratap Malla's entry into the throne is interesting as well as controversial.
III. His father's poor mental health made Pratap Malla rule as his regent.
IV. During Laxmi Nara Singh's reign, Pratap Malla became experienced in administration.
V. Pratap Malla kept Lalitpur and Bhaktapur divided using his tact.