Imoen is a character in the Baldur's Gate video game series known for her mischievous and playful nature. As a trickster, she often uses her wit and cunning to navigate situations and interact with others. This can sometimes lead to strained relationships with her friends, as they may not always trust her intentions or actions.
You just cast them like any other mage, select them from her spell menu. Be aware that mages can't cast spells while wearing anything more than the lighter pieces of armour. Normally a pure class mage can't actually equip such things, but the rule applies to dual- and multi-class characters too. Imoen is a Mage/Thief, so she can wear armour like chainmail, but doing so will disable her spellcasting abilities. Better to stick with things like Shadow Armour (+4 Leather Armour) or special Mage-friendly armour like Bladesinger Chain.
The playable NPCs are, Xzar (Human Necromancer) Monteron (Halfling Fighter/Thief) Jaheira (Half-Elf Fighter/Druid) Khalid (Half-Elf Fighter) Minsc (Human Ranger) Dynaheir (Human Invoker) Eldoth (Human Bard) Skie (Human Thief) Alora (Halfling Thief) Imoen (Human Thief) Garrick (Human Bard) Branwen (Human Cleric) Tiax (Gnome Cleric/Thief) Edwin (Human Conjurer) Faldorn (Human Druid) Quayle (Gnome Cleric/Illusionist) Safana (Human Thief) Coran (Half-Elf Fighter/Thief) Ajantis (Human Paladin) Kivan (Elf Ranger) Viconia (Drow Elf Cleric) Xan (Elf Enchanter) Yeslick (Dwarf Fighter/Cleric) Kagain (Dwarf Fighter) Shar-Teel (Human Fighter) The recent 'enhanced edition' adds, Dorn (Half-Orc Blackguard) Neera (Half-Elf Wild Mage) Rasaad (Human Monk)