Relm's Strength and Stamina are among the worst in the game, but her Speed, Evasion and Magic Evasion are above average, particularly for mage-type characters. Relm's standout stat is her Magic—at base 44 she has the highest Magic in the game, making her a natural fit to be a mage.
Relm's equipment draw is nearly identical to Strago's, with the addition of female-exclusive pieces and a pieces exclusive to Relm. She can equip Brushes, rods, maces, and some daggers for weapons, and universal shields, robes, and creature costumes for armor. She joins the party equipped with a Chocobo Brush, Mythril Shield, Plumed Hat, and a Silk Robe. Her ultimate weapon is the Angel Brush, won from the Plague in Dragons' Den. She also has an exclusive Relic, the Fake Moustache.
Relm's access to daggers and maces is largely irrelevant due to her poor physical stats. She can use magical rods to cast spells when attacking, and the Healing Rod can be used to heal party members without using magic or items, or used offensively against undead enemies. The Magus Rod offers +7 Magic and can be acquired early in the World of Ruin. Her various brushes offer lower Magic boosts, but boosts her other stats instead.
Relm's defensive options are light gear and mage robes, but in the late-game she has access to two powerful armor pieces, the Behemoth Suit and the Cat-Ear Hood. The Behemoth Suit is almost as powerful as Genji Armor and boosts all of Relm's stats by 6, and the Cat-Ear Hood grants Relm resistance to all elemental damage but water and poison, and doubles the amount of gil won from battles. With the Behemoth Suit and Cat-Ear Hood and a proper shield, Relm can be a very durable mage.
Relm's primary ability is Sketch, which lets her draw a living replica of an enemy to attack. In the vast majority of cases, when Relm Sketches an enemy, there is a 25% chance of one attack being used and a 75% chance of the other. There is, however, a handful of enemies in the game which always deliver the same attack when Sketched. The attacks usable via Sketch are usually attacks the enemy is capable of using normally. In the original Super NES release, Sketch was glitchy and the game could be corrupted if the wrong enemy was Sketched.
Sketch is largely useless due to the fact the attacks used via Sketch calculate damage based on the enemy's stats. Because of how Final Fantasy VI's damage formulas are balanced, enemies usually have far lower Strength and Magic than the party will, so even if Relm Sketched an attack that would be very powerful otherwise, it will be far less effective than expected. Many enemies have either normal attacks or their special attack as one or both possible Sketch attacks, including most bosses, with the notable exceptions of Kefka and the eight legendary dragons. Most of the time whatever attack Relm uses via Sketch will simply not be very powerful.
By equipping the Fake Mustache, Relm's Sketch turns into Control. When Relm controls an enemy, the enemy enters a Confuse-like state where their sprite reverses. Relm takes the same stance as when casting a spell, and on her turn she will have a unique command window with up to four commands usable by the enemy monster. When a command is input, the monster will use the command, and Relm's ATB gauge then depletes and refills as though she is taking her normal turns. If the monster dies or is struck by a physical attack, Control ends and Relm's ATB gauge depletes, and she will have her normal commands on her next turn.
Control is far more useful than Sketch in most situations. It can take a monster out of battle for several turns and turn their own powers against them. However, it is still preferable to teach Relm powerful spells and utilize her as a mage, since monster stats are still low and they will do less damage than Relm could herself. It is difficult to maintain Control of an enemy in a battle with primarily physical attackers, and most bosses are immune to Control.
Both Sketch and Control are useful as utility abilities to teach Strago Lores. Monsters that use Lores Strago can learn often have them as Sketch or Control abilities, eliminating the need to wait for the enemy to use the Lore so Strago can learn it.
If Shadow was not waited for before escaping the Floating Continent, Relm will gain the protection of Interceptor in his place in the World of Ruin. Interceptor will randomly intercept blockable physical attacks on Relm, nullifying their damage, and has a chance to then counterattack with Wild Fang or Takedown, which deal non-elemental magic damage to one opponent, but miss on Floating targets.
In the World of Balance, Relm joins the party in the Esper Caves. When the party battles Ultros, Relm will automatically arrive when his HP falls below a certain threshold, and after a cutscene joins the party. Using her Sketch ability on Ultros automatically ends the battle.
In the World of Ruin, the way to recruit Relm varies depending on whether the party waited for Shadow before escaping the Floating Continent. If they did, Relm can be found in Owzer's Mansion in Jidoor and will rejoin the party after they defeat Chadarnook. If the party did not wait for Shadow, Relm will be found in the Cave on the Veldt and the party must rescue her there and defeat the Behemoth King, after which she can be found in Owzer's mansion.
Relm must be recruited in the World of Ruin to recruit Strago. When entering the Cultists' Tower with Relm in the party, a cutscene will occur where she snaps Strago to his senses and he rejoins the party.
When the player revisits Thamasa with both Relm and Strago in the party, a cutscene initiates where Strago learns his friend Gungho has been hurt fighting the monster Hidon, and a cave on Ebot's Rock appears containing Hidon's lair. Relm must be in the party to initiate the cutscene, but does not need to enter Ebot's Rock to face Hidon, only Strago is required.
During the ending when the party is escaping Kefka's Tower, Relm's ending scene will be different if Strago was not recruited, where Edgar, Celes and Setzer run by her as she struggles to get down the conveyor belt, until she threatens to draw their portraits and they come back for her. Relm also appears in Strago's ending scene.