Energon / Superlink

Transformers: Energon (Transformers: Superlink in Japan) was the 2004-2005 Transformers toyline and animated series, another co-production between Hasbro and Takara and a direct sequel to Transformers: Armada. In this series the Transformer's big gimmicks are the Autobots' ability to combine with partners of the same size, the Decepticons' ability to use powered up forms, and the addition of Energon weapons and stars that can be placed on any Transformer. Minicons, from the previous line, are still present, but all Minicon pegs are "dead," and do not activate a function on the toy. (Wikipedia)