Find your tribe in a Sea of Creativity
Headcanon that sometimes Luigi helps with babysitting the Koopalings whenever Bowser needs it to be done (raising 8 kids all by himself is a huge job). Since Luigi is a plumber and works with technical stuff, I like to think that he helps Iggy work on his machines. Iggy isn't talkative at first. He prefers to work away from distractions and is extremely focused in his work (like ADHD-focused), but Luigi slowly allows Iggy to come out of his shell (pun intended).
Luigi listens to Iggy's info-dumping about science. He gets the whole machinery thing but he has no clue what Iggy is talking about science-wise. Sometimes the other Koopalings join in as well, and by joining in I mean Luigi trying to prevent them from doing mischief.