I've never really gotten the hang of same-wall

Plus is pretty simple. You just take the two sets of numbers that match when you put a card down, and if they both add up to the same thing, then it's plus. Like if you have an 8 on top and a 5 to the side and you play a card with a 5 on top and an 8 to the side. If you would've done a card with 8 on top and 5 to the side, it would've been plus.

Anyways, plus adds a value of one to all the numbers on the card you played, so if on the other side, it was a four touching a four, it would now be a five, and would flip the card with the other four. And then if that card could flip any with its base numbers (I don't think you add any in a combo at least) it will do that. You can pretty much turn over the entire board to your favor with plus combos