If you specifically aim to minimize Shuckle's speed, it can have as low as 13 at L100. That's low enough that a level 2 maximum-speed Deoxys-Speed can outrun it, and even at level 1 you can get a speed tie if Deoxys holds a Choice Scarf.
You can make Shuckle even slower by having it hold Iron Ball or Power Weight, either of which will reduce its speed to 6. At that point, a freshly hatched level 1 Buneary (among other possibilities) can outspeed it.