Grell are magical floating jellyfish. Usually these monsters rely on magical abilities rather than attacking.
In FFA Grell are found around Marsh Cave paired with Death Flowers. They do little more than float around.
In SoM Marmablues are classified as Fish.
Marmablue / Sailin’ Grell (J)
Marmablue are found in the Moon Palace and the areas occuring after it, aside from the Pure Land. The only thing they are able to do is cast MP Absorb. If they make a mistake and target the Hero they will take damage and he will gain a little life.
In SD3 Grell are classified as Fish.
In SD3 these jellyfish like enemies learned some new attacks, now they can attack with their tentacles as well as use some magic. They live inside the Seaside Cave on Bucca Island. They have an acid attack in which they will shoot a powerful acid gel at one of your characters. They also have a Funky Dance attack which should reduce your character’s max HP but actually does nothing. Their oil can be used to cast Aura Wave.
Grell Mages live in the Ancient Ruins of Light as well as in a ruins area inside the Mirage Palace. They have a Flash attack which will turn all of your characters into Moogles. Their Tricky Dance will reduce one of your character’s HP by 20%, they will always target the closest character to make it to them.
In LoM Tezla are classified as Morphs.
Tezla / Grell (J)
These monsters are mainly found on Madora Beach. They can attack with their tentacles as well as emit a stunning electric wave. As a pet it will defend you against Morph enemies.
Orc /Shore Grell (J)
This giant monster looks more like a strange shark and octopus mix than a Grell, but its Japanese name clearly links it to this family. It attacks on the S.S. Buccaneer after Elle and Gilbert are caught there by the Pirates. It can jab your with its tentacles and also shock you. Its Treasure Spit ability spews seaweed and treasure chests at you. It has a powerful Water Dive attack during which it will jump off the screen and then slam back onto you.