Games that require use of the GBA slot or other peripherals cannot be played on the New 3DS/New 3DS LL. But other DS/DSi games can.
At the very bottom:
http://www.nintendo.co.jp/3ds/new/qa/index.html
Also, the description for the game slot card on the Specs page for the New 3DS models says, "You can also use DS/DSi cards."
http://www.nintendo.co.jp/3ds/new/spec/index.html
Bro your Raichu is adorable I feel like reaching into the game & taking my Raichu out