1. Ross Youngs technically appeared in 10 seasons, but in 1917 that only consisted of 7 games.
2. Buzz Arlett had 469 plate appearances for in his MLB career over 121 games in only one season. IMO he is the player with the fewest "MLB" appearances who one can still make a credible argument for the Hall.
Here's a snapshot of Ross at Spring Training in 1925, about to go golfing I assume.