Level
6th
Casting Time
1 Action
Range/Area
90 ft.
Components
V, S
Duration
Concentration
10 Minutes
School
Evocation
Attack/Save
DEX Save
Damage/Effect
Slashing
You create a vertical wall of whirling, razor-sharp blades made of magical energy. The wall appears within range and lasts for the duration. You can make a straight wall up to 100 feet long, 20 feet high, and 5 feet thick, or a ringed wall up to 60 feet in diameter, 20 feet high, and 5 feet thick. The wall provides three-quarters cover to creatures behind it, and its space is difficult terrain.
When a creature enters the wall's area for the first time on a turn or starts its turn there, the creature must make a Dexterity saving throw. On a failed save, the creature takes 6d10 slashing damage. On a successful save, the creature takes half as much damage.
Just a wall of literal buzzsaws. Clerics are op.
Yes. If damage is from a spell, it is considered magic.
If it had a "friendly side" then the spell would say so; the three-quarters cover applies no matter what side you're on, as in both cases you're trying to attack through a literal wall of flying blades. It doesn't prevent you from seeing a target though, so if you have anything that can force a saving throw (ideally one other than Dexterity) then you can still use those.
When a spell effect appears, the creatures inside the AOE do not "enter" the spell effect. AOEs that deal damage when they appear say so. By comparison, look at Wall of Fire, which uses the phrasing "when the wall appears".
Creatures take damage from Blade Barrier if they enter the area on a turn: This means the wall exists, and they move from a space outside its area to a space inside its area.
Creatures take damage if they start their turn in the area: This means they are within the area of effect when their turn begins.
If you cast this spell such that a legendary creature is within the area, and they then use their legendary action to move out of the area, they would take no damage from the wall until they re-entered it.