Assumable mortgage and additional financing

[Vincent Claypole]

Hello everyone, 

I'm new to real estate investing and have been browsing bigger pockets for a couple years now. I cant quite find the answer I'm looking for so here's my question:

I have found an off market deal in my neighborhood and have formed a good relationship with the seller. He mentioned his loan is assumable and has a great interest, and he is all for me assuming the loan. However, the seller would need to sell the home for $100,000 more than the assumable loan. Does anyone have experience with financing in a situation like this? To my understanding, I would need to secure a loan in a second position to the assumable mortgage. Is sub2 a similar process? Or possibly even more of a simple process?

Thank you.