Reply to "how to carve pink foam"

For a straight line, I generally use a table saw with an old blade.  You have to maintain a firm stead grip yet be ready to run away if the saw grabs the foam, melts a bit of it to the blade and sends it flying.

For terrain, I generally use a keyhole saw and or pen knife.  A steak knife can also be used.  Shaping can be done with a wood rasp and or coarse sandpaper.  The wood rasp can also be used to smack against the foam to make “tool marks” in masonry.  A triangular file can be used to make mortar/joint lines in masonry.

And RSJB18 mentioned the most important tool: a shop vac.