Review the item:
Mike loves to play computer games, especially Tomb
Raider,
he imagines that all the villains are his problems, and he gets great
satisfaction blasting them to bits.
For a sentence to be fused, you must have two complete sentences run together with no punctuation. In the example above, a comma joins the two sentences. Mike loves to play computer games, especially Tomb Raider is one sentence. He imagines ... begins the second sentence.
Thus, the error is a comma splice.
To fix the problem above, you could put a period after Raider and begin he with a capital H.