Black ball

It's like Ryu vs. Akuma if they were robots.

Black balls (ブラックボール burakku bōru) are a mysterious and apparently super powerful energy source that, if possessed by evil-doers, could obliterate all life as we know it. So naturally, the Decepticons want to get their hands on them.

Fiction

PDTF Comic

Having discovered the power of the black balls, several Decepticon leaders and headliners from multiple eras joined forces to hunt them down and use their might to conquer the Universe. Multiple Autobot leaders and headliners from across the timestream also teamed up to try and keep them out of enemy hands.

Since the black balls look almost identical to cartoon explosives, the Autobots repeatedly used the tactic of disguising explosive decoys to dishearten/maim their opposition. Starscream seemed to be at the epicenter of each exploding black ball ruse.

Galvatron eventually managed to collect all of the black balls and used them to fashion a necklace similar to the bead necklaces worn by Buddhist monks (oh sweet irony). Galvatron swiftly lost his collection of black balls after being knocked out by Ultra Magnus's severed head. PDTF Comic

Legends comic

Black balls were miniature black holes that manifested within various Autobots and Decepticons when Scorponok chucked a bunch of explosives into a nearby giant black hole and blew it up. They slowly shrunk the Transformers' bodies by absorbing their matter, threatening to ultimately collapse in on themselves and take the victims with them. There was no way to stop the process, but since heads weren't affected and Headmasters could disconnect from their bodies, all non-Headmasters were converted into Headmasters and escaped certain doom at the cost of losing their bodies. Headmaster Chapter Prologue