Here are some monster abilities I'd like to see implemented in PE:
1. Burrow into the earth and emerge in different places on the battlefield, knocking anyone nearby back.
2. Swallow party members whole, they are paralyzed and take damage until rescued
3. Tentacles (or chains on a chain golem) that can grapple party members and hold/drag them until the tentacles are cut/smashed
4. Grappling with their entire bodies or otherwise directly hanging onto a party member
5. Leaping/jumping/pouncing creatures who can clear obstructions
And here is a monster with all of these properties packed together, just for fun:
This monstrosity is a giant blubberous red-veined worm, covered in wriggling, lashing tentacles and capped by a cone shaped circle of teeth. It is capable of moving rapidly and completely underground in its native environment, emerging only to surprise prey. When attacking, it uses its many tentacles to grab anything that might be food and swallows it whole with great zeal, a dull roaring sound emerging from its fearsome maw. This creature often carries active subdermal larvae, which can emerge if the parent becomes injured. These small juveniles, in a different part of their life cycle, have hard shells and somewhat resemble trilobites or hermit crabs. They are capable of leaping far distances and latching onto living creatures. Once attached, they use their mandible like proto-jaws to slowly burrow inside the victim, feasting on their flesh.
Though fearsome, encountering a full adult is quite rare as they tend to avoid civilized areas and can only be found in hotter/wetter climates. They and their young are vulnerable to fire, while the rubbery tentacles and hide of the adult can be easily severed with slashing weapons. Anyone who has been swallowed whole by the creature is trapped - there are backward facing teeth spiraling all down the creatures throat - however it can take a long time for victims to die and be digested, so if the creature is killed, these victims can be freed by cutting the worm open from the outside.