Being an instant isnt even that interesting here, since the addendum text encourages you to run it out during one of your main phases anyway
The undead have a way of doing that
No one way is better than another so long as it allows you to survive long enough to begin overpowering your opponents in the late game
You could also activate a tap ability in response to an attack, tapping a creature to gain some benefit before it blocks
By process of elimination you know that our top card is a Black legendary, but what
Oath of Ajani, Oath of Jace, Oath of Liliana, and Oath of Teferi: enhance planeswalker efficiency, provide protection, and allow double activations