[Banishment], 4th-level abjuration.
Its effect was to briefly banish one creature within sight to another plane (Charisma save).
After the duration ended, the target would be teleported back to its original location.
Without a doubt, this was an extremely practical spell.
Especially in a group battle where the enemies were numerous and elite individuals were present.
Imagine this scene: a well-equipped four-person adventurer party, while exploring a dungeon, accidentally encountered a troublesome monster capable of summoning large numbers of "grunt-type" henchmen.
Under normal circumstances, everyone in the party would need to deal with the encircling attacks of countless grunts while staying alert for the elite monster's ambushes. It was extremely troublesome.
But if the party had a spellcaster who had mastered [Banishment], they could directly cast the spell and banish the elite monster from the field.
Their teammates would then seize the chance to clear the battlefield.
When the spell's effect ended and the monster returned to the field, the monsters' original numerical advantage would no longer exist. The situation would be reversed, and it would instead have to face the adventurers' siege.
Some quick-witted groups with battle ingenuity had even developed a use for casting [Banishment] on themselves or their teammates to avoid potentially massive damage.
For example, the final Dragon Breath released by a great dragon that had exhausted every last ounce of strength before death; or a one-use [Sunburst] spell scroll from some wealthy mage.
The special effect of planar travel had allowed this spell, after countless years of development and use, to be played with in all kinds of ways by spellcasters across the world.
But in the end, it was only a fourth-level spell. This meant that, at minimum, a level 7 mage could memorize its spell model and place it on their regular spell