Yumi
Frost 
Back row 
Wizard Tier 0 Black Ice
Damage Dealt: Inflict damage equal to 1220% of Attack.
Target: All Enemies
Effect 1: Frost
Frost: Cannot take any actions.
Effect 2: Apply Buff
Target: Self
Change Appearance: Transform into a figure specialized for battles.
Frostwater Fan
Damage Dealt: Inflict damage equal to 720% of Attack.
Target: Forward All Enemies
Frost Empress
Effect 1: Status Effect Bonus Damage
Target: Self
Damage is increased by 50% when attacking a target affected by Frost.
Apply the following effect to Self at a 100% chance.
Skill Damage Increase: All skills Damage is increased by 50%.
Effect 2: Additional Damage
Activation Condition: Activates when you have 1 or more Frost Empress buff(s) cast by Self
Deals an additional hit equal to Attack 157% 1 time(s).
Slay Evil
Effect 1: Apply Buff
Target: Self
Critical Damage +88%.
Effect 2: Apply Buff
Target: Self
Critical Hit Chance +18%.
Character sizes
Recommended stats
About Ignore Damage Reduction %
This stat only works if the boss has passive skills giving him damage reduction. If not, it's useless.
Avalon, Reincarnation of Stars and Raids usually all have this passive, but always double check to make sure.
Recommended cards
Cards will always change depending on the stage and content you are currently facing, this is just a couple of examples on what cards work for this character.
Red Dragon's Blessing (Abyss Floor 60)
Attack +60%
Critical Strike Chance +10%
Queen's Temptation (Morgan le Fay)
Magic Attack +60%
Critical Hit Chance +10%
Elgrad Sword Art Journal (Lua)
Additional Damage +15%
Critical Damage +100%
Between Snowflakes (Yumi)
Magic Attack +60%
Critical Hit Chance +10%
Extra notes
Without sources of Freeze (skills, pets, Balisada, etc.) her damage tanks quite a bit. Merlin is enough to have 100% uptime, with the second best option being Balisada on your tanks.