Dweomormir’s Dimensional Lockdown

You snap a crushing lattice of runes into a translucent dome. The dome is centered on a point you can see within range and is impassable to teleportation or planar travel—creatures can’t teleport or plane shift into, out of, or through the dome.

• Casting Under Pressure. A creature inside the dome (other than you) that attempts to cast a spell of 1st level or higher must first succeed on a CON saving throw against your spell save DC. On a failure, the spell fails and the slot (or charge) is expended. On a success, the spell works but the caster takes force damage equal to twice the spell’s level.
• Boundary Seal. Spells and magical effects cannot cross the dome’s boundary; they only affect targets on the same side as their point of origin when cast. (Area effects that overlap both sides are split at the boundary.)
• The dome is not a physical barrier: creatures can move through it normally. It is opaque to ethereal travel.

At Higher Levels. When cast with a 7th-level slot, the radius becomes 40 ft; with an 8th-level slot 50 ft; with a 9th-level slot 60 ft.

“No lines in, no lines out. Your magic stays where it’s told.” - Dweomormir Slate