They have high stats for a Monster Class and is similar to the Dragon class, what with having skills of different Elemental Affinities for each tier. The Great Wyrm's special attacks have very large Area of Effects (the first skill has a 3x3 AoE), making them great for attacking large groups of enemies.
These are the strongest of all dragons. There are few of them left in the Netherworld, so little is known about these monsters, other than they have impervious skin and massive claws that can rip anything to shreds. Challenging them is literally suicide.
The Great Wyrms have the same 'set' of attacks, but each tier of Wyrm has a different elemental affinity. Efreet and Kagusutchi add fire to their attacks (So the Effect column would read not just 'ATK' but 'Atk/Fire'), and their attacks start with the word Fiery; Shaitan, wind element and Raging prefix; Marid, ice element and Frigid prefix; Flamberg, no element and Astral prefix; Surt, no element and Diabolic prefix.
3 x 3 Square in front of Great Wyrm
Fearful dance of the Great Wyrm
8 squares around Great Wyrm, but 'pushed out' one square away on the cardinals
Utter destruction caused by the Great Wyrm
Hits 9 squares in a triangle area in front starting at range 2 (1, 3 and 5 squares per row).