Command: “The spell has no
Effect..,if your command is directly harmful to it.”
Moving within Spike Growth causes damage. If you Command to flee, you are forcing movement that will cause damage; therefore the spell fails completely.
Command doesn’t say the target has to be aware of the danger. The target doesn’t lose a turn if there there is no effect.
The way I interpret it, the spell causes a
compulsion to flee, not the actual ability to flee.
Consider a caster that fails the save. He looks around at the spiked growth, and formulates a plan! On his turn, he casts
dispel magic to drop the spiked growth, and then moves away.
Now consider an ordinary goblin. He fails his save, looks around, sees he's stuck... and the spell fizzles, so he gets to act normally?
The goblin manages to evade
command when a wizard does not?
because the wizard is smarter and has access to an arsenal of spells to help him out?
I dunno... that doesn't make sense to me. From a narrative perspective, if nothing else, the goblin shouldn't fail its save, but then shrug off the spell anyway just because it's not sufficiently bright or well-equipped escape. It more interesting, imo, that the goblin might just fret that it can't get away while futilely using his axe to try to hack down the
spiky growth, or something.
And from a game perspective, I think it's a fair compromise. Eliminating the target's next action without causing harm or movement distance means the spell probably isn't as useful as the caster hoped, but it's still not a complete waste of the spell. And by keeping it situational, such a ruling also leaves future castings of the spell a little uncertain-- and therefore interesting.
YMMV.