(at around 54 mins) Thor's "friend from work" line about The Incredible Hulk was suggested to Chris Hemsworth by a Make-A-Wish child who visited the set on the day the scene was filmed.
Director Taika Waititi said in an interview with MTV News: "I would say we improvised probably eighty percent of the film, or ad-libbed and threw in stuff."
Sir Anthony Hopkins had decided against returning as Odin, but upon reading the story, he changed his mind.
In the Marvel Comics Universe when a being becomes the last of its race, the being is imbued with immortality and that being becomes part of a new race called an Elder of the Universe. That means they can no longer die and hence are immortal. It is how the Universe protects the last of a kind in the Marvel Comics Universe. The Grandmaster and The Collector are two examples in the Marvel Comics Universe.
Director Taika Waititi based Korg's character on Polynesian bouncers: "We wanted to change the idea of what a hulking guy made of rocks could be. He's huge and heavy, but with a light soul, and he's funny and friendly."
Matt Damon: (at around 10 mins) The actor portraying Loki in a play honoring the God of Mischief's apparent self-sacrifice in Thor: El mundo oscuro (2013). Damon also played an archangel named Loki in Dogma (1999).
Stan Lee: (at around 51 mins) Executive producer and co-creator of Thor and The Incredible Hulk appears as the barber who cuts Thor's hair.
Sam Neill: (at around 10 minutes) The actor playing Odin in a play honoring the God of Mischief's apparent self-sacrifice in Thor: El mundo oscuro (2013). Neill previously worked with Taika Waititi on A la caza de los ñumanos (2016).