This can be before blockers are declared, after blockers are declared but before combat damage is dealt, during combat after combat damage is dealt, during the postcombat main phase, during the end step, or, in some unusual cases, during the cleanup step
This efficiency is extremely relevant against all the above-mentioned decks, since they try to be as explosive as possible to overwhelm the opponent before he manages to stabilize
Update the app regularly to benefit from performance and security improvements
It can be hard to find what youre after since there are multiple Mystical Archive variants, but TCGplayer can show you listings from multiple stores across the country, giving you plenty of options to choose from
The +2 protects her and lets you get past your opponents flyers if youre playing Mono-Blue
I also want to piggyback on Brads comment above