Most of the time cards that have it end up having to be watered down or costed up dramatically, because when you don't do that then players have a tendency to die
Since you wont necessarily know when that opportunity will arise, leaving a large amount of mana available every turn might not be practical
This Spirit has got four wings, a snake-like body, two 'arms' and a head made up of only light
Note there are no breaks here like noncombat, or once per turn, or everyone like Furnace of Rath, your foes too
Level 1 Design: A Simple Rider This is how I expected Surveil to be usedthe same way Scry is
Unfortunately the card does miss on non-Legendary Creatures though, which contributes to why it isnt higher on the list