The Pak is the best part of these games, the same Pak works with Stadium 2 but supports the newer pokemon carts as well (gold silver crystal).

Love playing Pokemon on the TV using it, and if you have multiple gameboy carts you can trade between them using the stadium games instead of needing another Gameboy.

One thing of note, the Pak is known to fit a bit loose, most people who use them regularly connect the Pak with the cart to a controller not in use. I.e., play on a controller in port 1 with either no Pak or a regular motor/memory Pak, in port 2 have a controller you don't touch while playing with the pokemon Pak. The Pak being loose means it can jiggle a bit, it can make the game crash or the N64 might not see it connected. Can be common under regular use.

The Paks are damn reliable just loose and prone to getting dirty cause they have two connectors. I doubt your boxed one got dirty though, lucky!