First appearance of 24 and 21 in their permanent incarnations. There were earlier henchmen that had similar voices (most notably in Mexico) but this is the first time 24 is called by number and 21 has his pudgy appearance and squeaky voice at the same time.
The agent Brock runs into the woods is named Steve Sommers,it is the combination of the Six Million Dollar Man, and The Bionic Woman whose names were Steve Austin and Jamie Sommers. He also has bionics and speaks of having had $6 million spent on keeping him alive.
Hank's pajamas are based on Aquaman's costume & Dean's are based on Spider-Man's costume.
When Baron Underbite shows up to talk with The Monarch and they attack each other, after the Baron dispatches his attackers, he throws a metal sphere at Monarch which is one of the orbs from Phantasm, as a blade pops out of it while heading to the Monarch.