Cirno

Cirno is an early game unit with high health, attack power, and physical defense, but low speed and magic defense. Her special status effect "Frozen" is applied rather infrequently at an estimated 15% chance per hit, but its effect on the battlefield shouldn't be underestimated. She also has a relatively fast level growth, but isn't as quick as Daiyousei or Rumia.

Where to Obtain
Cirno and her spell cards are acquired from the Main Quest "Misty Lake," which is available on Easy difficulty to units level 3 or above. One of Cirno's rarer cards, Icicle Machine Gun, is found in the Main Quest "Forest Behind the Shrine" on Lunatic, which is the quest most associated with Rumia.

Strategy
Cirno's status effect prevents an enemy's behavior gauge from filling as long as it's active, effectively preventing the affected target from being able to act for a short time. This delay can be extremely helpful at times, especially when paired with other spell cards that prevent enemies from activating their attacks, such as Sakuya's bomb-deleting Eternal Meek. Icicle Fall, while weak, is an easy spell card to stack and is decently effective at keeping multiple enemy units frozen at a time when its aiming is set to random. Perfect Freeze's passive effect will apply to both normal attacks from blue-aligned characters, such as Tenshi, and also to blue-aligned spell cards, like Princess Undine, Icicle Fall?, or Luna Clock. Like Demarcation, Perfect Freeze's passive effect only lasts as long as Cirno is casting it, so replacing it with another active spell card will cancel the freezing effects from other units. Also, much like Demarcation, multi-hit spell cards are highly effective at freezing enemy units due to activating the unit skill, but Perfect Freeze is guaranteed to freeze enemies as part of its unique passive. Hailstorm itself is an effective counter, much like Eating from Rumia, but unlike Eating it is an active spell card which means it will no longer freeze enemies on contact if Cirno activates another spell card over it. Currently, Tenshi is Cirno's best teammate thanks to having two multi-hit blue attack spell cards that pair well with Cirno casting Perfect Freeze, but Sakuya's Luna Clock also has high compatibility with Perfect Freeze. Also, despite Icicle Machine Gun having a highly appealing effect, it is extremely difficult for Cirno to take advantage of it right now because there are no other units at this point in time that can freeze units without the help of Perfect Freeze, and activating Icicle Machine Gun disables Perfect Freeze's effect if it has been active.