Crystals

The Elemental Crystals are four enemies encountered in battle alongside the optional boss Culex in Super Mario RPG: Legend of the Seven Stars. They include the Earth Crystal, Fire Crystal, Water Crystal and Wind Crystal and are so named due to their elemental nature. Like Culex, they are from the dimension of Vanda and met in a portal leading to that world found in Monstro Town.

Each of the crystals has a different choice of attacks and range of stats, as well as a theme in attacks used. These differences all lead to varying levels of difficulty in battling each, as well as different appropriate battling-strategies.

Earth Crystal
The Earth Crystal has the highest amount of HP out of all of the four crystals, but balances out with a dismal defense of 70.

Despite being the crystal of earth, it only has two earth-based attacks, Boulder and Sandstorm. It also wields Storm and Water Blast. It finishes up with the move Blast.

It is weak against Thunder-based attacks.

Fire Crystal
True to its name, the Fire Crystal uses largely fire-based attacks, including Corona, Flame, and Flame Wall. It rounds these attacks out with the moves Drain and Mega Drain.

It is weak against Ice-based attacks. It has greater Magic Defense than the next-in-line Water Crystal. Combined with its exceptional Magic Attack, it can be considered an even more difficult opponent than even the Earth Crystal.

Water Crystal
The Water Crystal is the second-to-last crystal (right above the Wind Crystal) in terms of weakness. While wielding decent Defense, its Magic Attack and Magic Defense are still lower than that of the Fire Crystal.

It uses mostly ice-based moves, namely Ice Rock, Blizzard, Crystal and Solidify, as well as the non-elemental Diamond Saw.

Its only weakness is Fire-based attacks.

Wind Crystal
The Wind Crystal is the weakest of all the crystals, but has massive physical defense, making it take far longer to defeat than the others.

The Wind Crystal has mainly electrical-based attacks, such as Bolt, Electroshock, Lightning Orb and Static E!. It also has two attacks that may inflict status effects on Mario and his party. Petal Blast causes the entire party to transform into mushrooms, which prevents any party member from attacking or using an item, but heals a small amount each turn.

The Wind Crystal is also armed with the Light Beam attack, which leaves the party under the sleep status. Once defeated, the Wind Crystal will disappear like the other three crystals until the battle ends.

It is weak against Jumping attacks, making it the only crystal susceptible to physical rather than special attacks.

Trivia

 * All four of the Elemental Crystals originally appeared in Final Fantasy and also featured prominently in Final Fantasy IV, from which Culex's theme music comes.
 * Paper Mario, a game once conceived as a sequel to Super Mario RPG: Legend of the Seven Stars, has the Crystal Bits serving much the same purpose and appearance as the Elemental Crystals alongside the Crystal King.