Patchouli

Patchouli is the only unit currently capable of shooting attacks from every attribute color, giving her a unique multi-purpose role in a party. Her unit skill adds 0.2 to her base attack power per spell card in the hand, so having no cards in the hand leaves her at base power while conversely she attacks at twice her base damage when the team has five spell cards in the hand. This makes her a damage powerhouse, especially when combined with her spell cards' passive amplification effects, at the cost of her being a slow-to-act unit. Her level growth is moderately slow.

Where to Obtain
Patchouli has the most spell cards in the game as of the most recent update, with most being acquired from the Main Quest "Voile the Magic Library" on its various difficulties, which is open to units level 7 and up on Easy difficulty. The Event Quest "Patchouli's Counterattack" also contains guaranteed spell card drops for Patchouli, which means as a unit she can obtained there as well with units level 5 and up on Easy.

Strategy
Patchouli is a powerful and flexible unit that likely will become even stronger of a party member when single-color teams are possible. Besides having a strong base ATK stat, her unit skill regularly buffs this already high stat if the player keeps spell cards unused in the hand, and all of her spell cards besides Philosopher's Stone are effectively at 2x the power due to their passive amplification effects e.g. Agni Shine is 400 power and Silent Selene is 800 power. Despite Philosopher's Stone not amplifying itself in the same manner as her other cards, it still does increased damage above its base power if it hits matching enemies, and only purple and yellow enemies are unaffected by it. Besides amplifying Patchouli's attack power, it is important to note that all of Patchouli's cards except for Philosopher's Stone amplify the attacks of team members as well as long as they are attacking with the same attribute. For example, an active Princess Undine will amplify the regular attacks of Cirno and Tenshi, and will amplify the attacks of blue attribute spell cards, such as Daiyousei's Icicle Fall? and Sakuya's Eternal Meek, effectively doubling them as well as its own power. Also, perhaps unexpectedly, Patchouli does not have a low base health, so she is surprisingly hardy with her greatest weaknesses being her low attack frequency and lack of multi-hit spell cards. Despite those weaknesses, she is perhaps the most versatile unit currently available in the game, along with the most customizable one.