Doppleganger Spell seems to not work as described.

[nepereta]

Had trouble with Doppleganger says in the wiki it behaves a bit like phase shift. In that you can go through walls etc. In practice I found it impossible going through walls.

[Roomba]

Yeah, the phrasing for doppelgänger seems a bit misleading.

[Convair880]

Doppelgänger allows you to phase through windows, doors and solid (as in density = 1) objects, but not walls. The incorrect description has been around since the first version of the page, but should be fixed shortly.