Winning the 5 toss-up states, flipping PA, and then flipping literally any other state, like AZ, WI, MI, or NV.
PA had one of their prominent newspapers that hadn't endorsed a Republican candidate since 1972 just endorse Trump, and searches for "Can you switch your vote" spiked in PA after the last debate, so PA is not a foregone conclusion.
GA, NC, and MI have sizeable black populations that are predicted to vote more in favor of Trump than any R candidate before. Probably still not a majority of the demographic, but enough to hold leads that were had in 2016.
Tldr - On my watchlist:
Obviously, the easiest path is the one I described, but if PA is flipped but FL is lost, we can flip MI and WI and then any of the Rocky Mountain states leaning Biden, but the ultimate middle finger of 2020 would be ME's 1 tossup district going to Trump, NH and PA flipping, FL to Biden, and then flipping MI and WI, giving each candidate 269 votes and sending this to the House. Where, by the way, each state would just get one vote, ending in a narrow Trump victory (29 - 21), but it would just be the chaotic cherry on top of this awful year.