Complex sentence: However, the princess saw through the wizard's trickery and when he offered her the bowl of potion, she threw it on a big boulder nearby and as a result the boulder started rolling down towards the wizard and crushed him.
Split into simpler sentences: However, the princess saw through the wizard's trickery, and when he offered her the bowl of potion, she threw it onto a big boulder nearby. As a result, the boulder started rolling down towards the wizard and crushed him.