First of all you have to catch a cubone in the Lavender town memorial place.
Then train it up to level 28 where it will evolve into Marowak!
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You cannot catch it without cheat codes because the Marowak is a scripted special Pokemon "ghost." If you really want a Marowak, you can get one by evolving a cubone or catching one on Victory Road.
You can catch marowak in the Pokemon Tower (with all the graves) yet they are quite rare. You can also evolve cubone. The Marowak that blocks entry to the top floor is uncatchable, and even a masterball (only obtained by hacking at that stage of the game) will fail.
Marowak cannot be caught in the wild in Pokemon Platinum. You'll need to capture a Cubone, which can be caught in Route 203 when there's a swarm of Cubone. (You'll need to talk to Lucas'/Dawn's sister in Sandgem Town) When it is captured, you can evolve it into a Marowak at level 28.
You must catch a wild Cubone or Marowak in Rock Tunnel with one, or use Thief to steal it from said wild Cubone or Marowak. There is approximately an 8% chance for them to have it.
Meowth is not in the wild in Pokemon Yellow. You have to trade to get it