At first, he seems a little more polite than Demolicious, which is not saying very much. He seems to soften up a little bit by letting the player help in the park war, if they choose to do so.
Later on, if the player decides to assist him in the apartment missions, Luigi complains that the malachite doesn't work as expected. He wants his brother (along with everyone else) to bow to his might.
Luigi also thinks very poorly of his robotic and human minions, although he claimed that numbers were the most important thing in victory.
Malicious Slander: He accuses Demolicious of wanting to sell the Pandorian Malachite for her own selfish desires, and it is implied that the other heroes no longer respect her as a result. Without EVEN trying to ask her what she actually wanted to do with the malachite when they got back to Herospire.
Take Over the World: That is, if he can use the malachite to revive his brother. He fails to revive said dead brother.
"The Reason You Suck" Speech: He declares that Demolicious wanted to sell the heart for her own selfish desires, while she is hanging from a pair of his robots that grabbed her arms. He's only half right — the reason she wants to sell it is for money to help her sick dad.