Sunstreaker was the first blow, when the orders came down. That might not have been Soundwave's intentions; almost certainly it went against Megatron's wishes. But the spy had taken far too much criticism and abuse from the arrogant former gladiator to not strike out personally. It had taken very little preparation for the racks Sunstreaker preferred to use to be rigged with quiescent bombs, explosives that would go active only once Sunstreaker reached a certain point in his self-loving routines.
It was an added bonus that the blast caught Sideswipe on his way to help with the polishing efforts.
The explosion rumbled out and pandemonium ensued, while Prowl tried to marshal the forces of the Ark into something cohesive to battle their unknown assailant. Scanners went wild, hunting high and low for Laserbeak, Ravage, or any of the other usual infiltrators. Autobots paired up to search.
The spy was partnered with one of his own kind, the one he most resembled, save for color. Admittedly, Bumblebee was the most trusting of the Autobots to begin with. It didn't take much to deactivate that innocent mech. Then the ruse was on, as he came across Mirage and Tracks, getting in close as his energon-splattered frame attested to some horrible run-in.
Mirage managed to get free enough to sound the warning, but the noble nor his partner were going to be of much use in the battle descending on the mountain.
After, when the fighting had cleared, and the Decepticons stood victorious on the remnants of the Autobot headquarters, Megatron smiled at his infiltrator.
"Good job, Cliffjumper. And, in keeping with the customs of this quaint world, I do believe I will say goodbye!" The cannon fired once, before Cliffjumper could even dodge, his processor failing him in that moment of awareness.
"He could have been useful against the ones who were not here, Megatron!" Starscream screeched at him.
"I only have room in my ranks for one known traitor, Starscream," Megatron assured him, before taking to the air, whirling his morningstar in complete pleasure at the day's events.