Mrs. Teachdevil is a tertiary antagonist in A Day with Bowser Jr. 

Mrs. Teachdevil as in episode 1

First episode

She gives the class a test in Part 1, which they have to complete before the bomb detonates. Her test is what caused Bowser Jr. to plan to leave the airship in Part 2. In Part 3, Bowser Jr left the airship, but his parachute was cut with scissors that a Lakitu was holding.

Two Koopas for a Throne

She makes a small appearance as a minor character. She is speaking when a stone hits her, knocking her out. It is unknown if she is alive or dead, or if she just lost consciousness.