The AL Central and the Wild Card race
Those pesky AL Central teams. The Mariners haven't played well against the Royals, Twins, or Tigers this year, and it is going to cost them. Well, it already has, technically. The Mariners are 6-13 against them. Even if they were to sit a game under .500 against them at 9-10, they would be sitting all alone in the WC #2 spot, ahead of all three of them.
Instead, they are looking up at them, and don't hold a tiebreaker over any of them. They are 1-5 against the Tigers, 2-5 against the Twins, and 3-3 against the Royals. The Royals, however, have a better Intradivision (within your own division) record, and would hold that tiebreaker too. Unless the Mariners went 6-0 to finish the season and ended in a tie with the Royals and shared an Intradivision record... they would still lose the next tiebreaker of Interdivision (against other AL teams outside your division) record, with the Royals at 30-34 and the Mariners at 27-37.
Really, it means that the Mariners have a lot that needs to go their way in order to make it. They need to finish AHEAD of two of the AL Central teams. They can't tie with them, or their out.
But hey, wouldn't that be the most Mariners thing to see this year? Watching them go 6-0, losing the AL West by a single game, and then tying with the AL Central teams only to lose the tiebreaker to all of them? Let's hope it doesn't come down to that.