Mark Wahlberg asked Sean 'Diddy' Combs to appear on short notice, with Combs flying over from Europe just to make his cameo. Doug Ellin didn't even have a scene prepared for Wahlberg and Combs, so they improvised most of the dialogue on the spot. Also, Combs does not know how to play golf.
Even though he was not required on the set at the time, Jeremy Piven was still present for Lenny Kravitz's scene in temple not only to help Kravitz understand the other side of his phone conversation with Ari but also because Piven is a fan.
Billy Walsh turns his back to the camera revealing his Medellin tattoo including the face of Vincent Chase as Pablo Escobar. Walsh had the tattoo done in The Dream Team (2007).
When E is in bed he has a massive hole in his PJs under his left arm