Simplify the following text for a Grade 7 native English-speaking person.
Original: As well as working as a standalone game , through a system dubbed `` lock-on technology , '' Sonic & Knuckles acts as an expansion pack to both Sonic the Hedgehog 2 and Sonic the Hedgehog 3 , with which it was developed in tandem .
Simplified: Sonic & Knuckles is an expansion pack for the video games Sonic the Hedgehog 2 and 3 .