Should Feather Step, a level 1 spell, help against even the most severe kinds of difficult terrain and hampered movement, such as deep bog?
A square that is part of a deep bog has roughly 4 feet of standing water. It costs Medium or larger creatures 4 squares of movement to move into a square with a deep bog, or characters can swim if they wish. Small or smaller creatures must swim to move through a deep bog. Tumbling is impossible in a deep bog.
For the duration of this spell, the subject ignores the adverse movement effects of difficult terrain, and can even take 5-foot steps in difficult terrain.
I think it would be reasonable for the GM to say that a deep bog isn't just difficult terrain, it's something worse, so feather step doesn't help.
I think it would be reasonable for the GM to say that a deep bog isn't just difficult terrain, it's something worse, so feather step doesn't help.
Right, I think I agree. What I'm considering is to say that Feather Step allows you to ignore difficult terrain that only halves movement.
Suggestion: If the terrain you're in causes one-quarter movement or less, Feather Step may not help, or may lower the penalty by one step (for example, from one-quarter movement to half movement).
What do you think?
I think of Feather Step as allowing you to move like Legolas in Fellowship of the Ring where he walks on top of the deep snow while everyone else has to push their way through it.
I don't think you could do that with four-foot-deep water (without a Water Walking spell).
In terms of game balance, deep bogs aren't so common in most games that it matters much one way or another.
I think "Feather step doesn't help at all" is more 'RAW' than "Feather step reduces it to regular difficult terrain" but either of your suggestions should be OK.