Complex sentence: Megatron found many stasis cells containing Autobot Elite Guard members, most likely placed on board the "Nemesis" to guard the prisoners, and had them also placed in Vehicon bodies, reformatting them into the Constructicons.
Split into simpler sentences: Megatron found many stasis cells containing Autobot Elite Guard members. Megatron believed that they were most likely placed on board the "Nemesis" to guard the prisoners and had them also placed in Vehicon bodies, reformatting them into the Constructicons.