Paul Rudd really did learn close up magic for this movie. "I really did learn some of the magic. I haven't really kept it up. But then again, trying to learn to be really good at magic in a short amount of time is like trying to learn violin in a short amount of time."
Langston Fishburne, Laurence Fishburne's son, played the younger version of his character, Dr. Bill Foster, after which his father's young face was applied to him by CGI.
(at around 32 minutes) Scott grumbles that just wearing a hat and sunglasses does not conceal your identity. This has been a running joke among fans, since several MCU characters have used this technique including: Captain America, Iron Man, Thor, Black Widow, Winter Soldier, Scarlet Witch, Nick Fury and Falcon.
The alien-looking organisms in the microscopic realm (on the way to the quantum realm) are water bears (tardigrades), which have been found in the most extreme environments on Earth including hot springs, glaciers, the top of the Himalayas and deep sea trenches. They can go dormant without food or water for decades and survive incredible temperatures, pressures, radiation, toxicity, and even several days in space.
The idea that Scott had some kind of encounter with Janet while in the quantum realm was suggested in the first film by way of a brief glimpse of a reflection on his helmet. It's unclear as to whether it's an angel, a blob, or Janet, but here it's confirmed that it was actually her.
Stan Lee: (at around 1h 21 minutes) When Wasp is firing shrinking disks at her pursuers, she accidentally shrinks the Ant-Man co-creator's car; Stan then says in response, "The 60s were fun, but now I'm paying for it" (thinking he's having an "acid flashback" - hallucinating from the drugs he used to use). Ironically, during the 60s, Stan was a huge opponent of recreational drugs, and even published such anti-drug messages within his comic books.
Gregg Turkington, Tim Heidecker: hosts of On Cinema (2012) have cameos in both Ant-Man films. Turkington as Dale from Baskin-Robbins & Heidecker as Whale Boat Captain Daniel Gooobler.