Boston to Philly using only transit

I came up with this question & wanted some answers from more knowledgeable folks than me. This is a hypothetical situation for reference but I still wanted to ask it. I have a good friend of mine that moved to Philly. If i wanted to use all local transit to get to Philly, excluding amtrak, what are my best options coming from Boston? I'm not familiar with septa or njtransit. Has anyone here done this route before? If so, what was your route? Do you count taking buses like greyhound or Peter pan? Those are the only options in MA since you can't take commuter rail to Springfield or CT. Insight appreciated. Discuss away.