As with Armada, these features comprised a variety of ways to “power up” the Transformers. However, Energon featured two main themes: weapons and power-ups made of the translucent plastic “Energon”, and multi-figure combination. Though the size classes were renamed and reshuffled, each class had a standard set of features once again. The smallest figures came with a weapon made entirely of the translucent plastic energon, as well as an “energon chip” which could be attached over a special peg with the character's faction logo. Deluxe and larger toys did not feature the energon chip, but still had the special receptacle. The larger Autobots could transform into the legs or upper body of a larger figure, and combine with one other such figure either as the top or bottom half. Many also featured translucent weapons. The largest Autobots included a weapons platform with which they could combine in robot mode to a “brute mode”. The Decepticons, however, were less themed, including only the occasional translucent weapons. As with Armada, many of the larger figures included electronics, though most were powered by “AAA” batteries, rather than button batteries, requiring large parts of the figure to be used as a battery box.
The series produced the first new sets of “free-combining” combiner teams, in which any limb robot could become any limb of the larger robot. Further, limb members of different teams could interchange. However, each team only had three unique molds, with the remaining two being redecoed limb robots.
Like most series of in this era, the line featured numerous redecoes, including multiple versions of almost all the new toys introduced. Only a few redecoes from previous series were included, and unlike Armada, these were not modified to fit the Energon series themes. Though Armada Unicron was one such redeco, the new deco was much scarcer than the stopgap reissue of the previous series' version. Energon ended in 2004, ready to segue into the final installment of the Unicron Trilogy: Cybertron.