The cards chosen also do a good job of capturing Karlachs strengths and personality
Crypt Incursion Crypt Incursion can be dicey since it relies on your opponents having creatures in the graveyard, but you only need to hit three or four creatures for this black instant to be a worthwhile investment, plus you get some incidental graveyard hate
Darksteel Juggernaut got cut from the list when my five-mana slots were overflowing with good choices, but I like the cheapness of Myr, the vigilance of Sentinel, and the flying of Gargoyle
You may choose a new target for it
For example, Dig Through Time's mana value is 8 even if you exiled three cards to cast it
My gut is leaning toward the former, since Azorius doesnt have Hallowed Fountain or any new cards from Guilds of Ravnica