Change your preferences here.
If held by Cubone or Marowak, this item doubles the holder's Attack stat. No effect if held by any other Pokemon.
The only thing that makes Marowak (and Cubone in Little Cup) even remotely usable. Marowak is otherwise a rather forgettable Pokemon, but with what is effectively an automatic Swords Dance boost while retaining the ability to switch moves (and in particular, the capacity to use Swords Dance itself), it becomes an immediate powerhouse. There is no other item that your Marowak should use over this—of course, this is assuming that you are using Marowak at all, as it is quite often forgotten in favour of other, bulkier Ground-types, as nobody could accuse it of not having enough power.
Route 13 (talk to Treasure Hunter - you receive one random treasure every day).
Wild Marowak (5%).