The gimmick here is that all twelve boulders start on the same spot. You must carefully unstack them in such a way as to leave the level solveable.
This solution is tested and verified to work.
Stacked Dozen
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Target Positions
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| . . . . . . . | | . . M K . - . . . . D . |
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Step One: Unstack A, B, C, D
  1. Push A one east, one north, four east, two north to position A.
  2. Push B one east, one north, six east, two south to position B.
  3. Push C one east, one north, six east, two north to position C.
  4. Push D one east, one north, four east, one south, three east to position D.
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Step Two: Unstack E, F, G, H
  1. Push E one east, one north, six east to position E.
  2. Push F one east, one north, five east to position F.
  3. Push G one east, two north, two east to position G.
  4. Push H one east, one north, two east to position H.
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| . . . . . . . | - - . . - - A . C . . |
| . . . < . . . | - - - . . . G . . - . | . |
| . . . . . . . | | . . . . . H . . F E | . |
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Step Three: Unstack J, K, and L from M
  1. Push J one east, two north, one east to position J.
  2. Push K one east to position K.
  3. Push L one north, one west to position L.
  4. Boulder M is already in its target position.
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| . . . . . . . | - - . . - - A . B . . |
| . . . < . . . | - - - . . J G . . - . | . |
| . . . . . . . | | . L . . . H . . F E | . |
| . . . . . . . | | . . M K . - . . . . D . |
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Step Four: Clear M, K, L, H
  1. Take M south then west to the first hole.
  2. Push K one west and take it like M.
  3. Push L one east and take it the same way.
  4. Push H three west, then south and take it.
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| . . . < . . . | - - - . . J G . . - . | . |
| . . . . . . . | | . . . . . . . . F E | . |
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Step Five: Clear J, G, and D
  1. Push J three south, two west, and take it.
  2. Push G one west and take it like J.
  3. Push D four west, one north, four west.
  4. Push D south and take it.
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| . . . . . . . | | . . . . . . . . F E | . |
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Step Six: Finish
  1. Push B one north and take it like D.
  2. Push A three south and take it the same way.
  3. Push C two west and take it like A.
  4. Push E one south and take it west like D.
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