The Artifact: The finale "The End of the Power Rangers" seems like an odd title to name a season that had 12 seasons and counting following it, but this was originally going to be the final season of Power Rangers before Disney was convinced to move production to New Zealand to save cost.
Channel Hop: How the producers got away with a lot of the season's Family-Unfriendly Violence. They told the first network (Fox Kids) that Cole's parents would've later turned out to be alive. They then "neglected" to tell the second network (ABC Kids) that the death had ever happened, so they didn't have to keep the promise, and they stayed dead.
Executive Meddling: Apparently, Forever Red was going to be a two-part episode that would have ended with the rangers summoning their respective megazords and taking down Serpentera together. Disney however did not like the idea of spending money to create the CG zord footage as they didn't have toys to promote and told them to cut it into one episode as the team-up was just expensive in general.
More meddling came from Bandai, the company that produces Power Ranger toys. After Disney refused to fund Forever Red, the writers asked Bandai for money. They agreed, but only if the episode promoted the Wild Force Rider toy, which is why Serpentera, Lord Zedd's most powerful super weapon, gets taken out by a motorcycle...
Name's the Same: The lead general of the Machine Empire in "Forever Red" is named Venjix, which is later used as the name of the main villain in Power Rangers RPM.
One of the Mutorgs from "Reinforcements From The Future" was Deviot's monster form from Power Rangers Lost Galaxy recolored. (They were originally going to use the Orgs from the Gaoranger movie, but they were lost in a fire.)
There are officially 100 Power Animals, but we only ever see 22. Toei actually designed and detailed about a dozen more exclusively for Wild Force, including a peacock with many weapons as its tail feathers and a wallaby with a baby in its pouch. These can be found in the artbook Super Sentai Robot Art Collection.
Forever Red was originally going to be two parts, though it was forced to become only one part thanks to the fact that another crossover, Reinforcements From the Future, happened recently, not to mention that it was two parts long. Many things were cut out of Forever Red, most notably the original fight with Serpentera.
Rocky (the second Red Ranger in Mighty Morphin) was originally scripted to appear in the episode. Unfortunately, Steve Cardenas was in the middle of moving and changing addresses after the producers first contacted him and he forgot to tell them. They couldn't recontact him so they had to do the episode without him.
Much of the Ship Tease in this season was supposed to have an actual payoff, with Danny going back to the flower shop with Kendall and Cole and Alyssa being married in a Distant Finale.
The teaser for this season shown after "The End of Time, Pt. 3" showcased an opening theme completely different from the final, presumably not used due to rights issues from the Power Rangers franchise's sale to Disney.
"Reinforcements From the Future" was supposed to use the Three Org Brothers suits from the Gaoranger movie as the Mutorgs which were unfortunately destroyed in a fire.
Rumours suggest that had the transition to Disney not been made and Cole's parents needed to not be dead, it would have been revealed that Jindrax and Toxica were Cole's parents transformed into Orgs.
A Where Are They Now scene for Cole was filmed, showing his new life as a veterinarian, but ultimately went unused.