omg....I totally forgot two or three very unusual ways to score.
A team could intercept the two point conversion and run it back for their own 2 point conversion.
A team could block a field goal and return it for a touchdown.
A field goal attempt could fall short, get caught like a punt, and returned like a punt for a touchdown.
I like the option of taking a free kick as the receiving team on a kickoff if you call a fair catch.