Why Fear a KNIGHT when you have a QUEEN (IS3 D15)

IS3 D15, Triple Ending (Gravestone + Knight + Skadi).
The Last Knight has 290000 HP and 5520 DEF, and inflicts a 2 second Cold on allies that attack him, which becomes a 4 second Cold when under 50% HP. Furthermore he becomes unblockable in phase 2. Due to how difficult it is to damage him, most Knight clears involve a permastall for both phases, but thanks to Schwarz and Kalt'sit, bursting phase 2 is also a viable strategy. On top of that, Gravestone and Ishar'mla are no pushovers either, but anything is possible when we have the power of Snipers on our side.
Rules:
1) Must defeat Gravestone
2) Must defeat The Last Knight
3) Must defeat Ishar'mla, Heart of Corruption
BGM
愚人曲 - Steven Grove
Promise (東方とにとりがゲッダン ver.) - Hirose Kohmi
The Firebird - Igor Stravinsky
Star Sky (French ver.) - Poucet
Dance Through the Danger - Cristina Vee
Determination - Intelligent Systems (Fire Emblem Sacred Stones OST)