Instead of transforming into vehicles they instead transform into animal like forms. The original Terrorcons could combine themselves to form one massive Terrorcon called Abominus, in much the same way as the Constructicons formed Devastator.
The original Terrorcons were part of the Decepticon faction during the great war.The original Scorponoc later joind them after the war ended, reforming them with the intention of reignighting the great war.In the Energon continuety however the terrorcons were a primitive race of Transformer, whose planet was consumed by Unicron, but whom Alpha Quintesson had recreated as worrior drones to collect enough Energon to reawaken Unicron and rebuild Alpha Quintessons home world. Later after gaining control of unicron, the reborn Megatron (and later Galvatron) would take control of the Terrorcons. These Terrorcon's however could not combine and were barely sapient.