Originally posted by Bravely Bold Sir Robin:

All fulings take poison damage. Lox take poison damage. Wolves take poison damage, so do drakes (tested with draugr fang). It's only really swamp creatures that don't take poison damage, and that makes perfect sense (they take spirit damage to compensate). I haven't tested on mistlands creatures yet, but if seekers are all immune to poison, I doubt dvergr are, and ashlands creatures almost certainly won't be.

IDK about the mistlands enemies, but 8 enemies are resistant (half damage?) to poison, 13 enemies are immune, and 3 bosses are immune. Also, damage over time will always be worse than up-front damage because you have to wait several seconds for the full effect and it's often wasted because you just hit them again before it'd run its course, killing the enemy.