I've used it to turn a PC into a frog in combat. One cast the spell, a second picked it up and put it in an opaque jar, while the third put it with a bunch of similar jars (and cast a spell). The PCs couldn't figure out which jar had the PC during the fight, so they were down one for the fight.
Giant Shark is the easiest option, however. It can survive for several minutes before suffocating, as well as having a huge number of HP. So long as the caster doesn't actually get close enough to allow it to attack (it has speed 0), the PC is effectively eliminated from the combat. I considered Giant Octopus at first, but it does have speed 10 and a reasonable attack.
Giant Shark is the easiest option, however. It can survive for several minutes before suffocating, as well as having a huge number of HP. So long as the caster doesn't actually get close enough to allow it to attack (it has speed 0), the PC is effectively eliminated from the combat. I considered Giant Octopus at first, but it does have speed 10 and a reasonable attack.