Confirmed: You can beat coop by yourself (spoilers)
Not that anyone cares, but for you anti social folks, I beat co-op split screen today by myself with two controllers.
There were four hard parts involved. Definitely doable.
Very early stage where you have to hit four switches in a row (2 per players)
Every other problem occurs in the final course.
Later level stage where you have to use the box to redirect lasers at the turrets. Tricky to get the timing down, but entirely doable.
The next to last section was very difficult with the bridge and grabbing the box. <- this was the level that took me by far the longest. I think that If I had a 2nd player to just hold the forward button it would a lot easier.
The very last level with the sliding box, creating the bridge. The problem is that player 2 can run forward, but player 1 needs to drop the box down the slide, and then catch up to the bridge. Again, it wouldn't be very complicated for a non gamer to walk forward for you.
Basically, you just need to have a plan in mind. Only a few sections in co op actually require you to be synchronized. None of the game requires you to have two players that know what they are doing.
There are only two online based achievements. One is the professor portal, the other is hug 3 friends. Both are very easy to boost for, although I would recommend trying to boost for professor sooner than later, once this game gets older it will be harder to find people who are playing their first game online.
I have every achievement (entirely playing solo) except for:
Triple Crown: I'm not sure where the game freezes the timer, if it is when you solve the puzzle or when you get both players to the elevator room. If it is the later, that is what really slows me down on these. I still think it is possible solo co-op splitscreen.
Completely doable solo. I just haven't gotten around to it yet.
Friendlist with benefits:
I will probably try to boost for this one tomorrow.