stuart haffenden(Pathfinder Roleplaying Game, Adventure Path Subscriber)
If someone within the area of a black tentacles spell isn't successfully grappled is their movement impeded in any way?
If you roll poorly during the turn that you cast this spell it's quite possible that every creature within the area could simple walk out at normal speed?
That's about the shape of it. Perhaps you'd be well-advisted to team up with the team Druid for a Sleet Storm or Entangle, or have a wand-wielding familiar pair your tentacles up with Grease.
Maezer(Pathfinder Roleplaying Game, Adventure Path, Companion, Modules, Battles Case Subscriber)
The last sentence of the description is:
"The entire area of effect is considered difficult terrain while the tentacles last."
So any non grappled target has their movement impeded, though most people can probably get out if they try.
Ah, missed that part. *Would still probably do the Grease thing, to be safe.*
Lessee. 20' burst, half-movement through difficult terrain, most enemies move at about 30' or better. Yeah, most of 'em can get out with a double move, though they'd pretty much be giving up their turn to do it, which isn't all bad.
Teaming up with someone who can cast Acid Fog is pretty effective, too. The fog caster just needs to ready an action to cast their spell the instant the Tentacles spell goes off. Solid Fog works for lower levels too, just not as nastily.