Columbium. 

You have it, twyngwyn.

 

Mysterious knight wearing Byzantine sapphire (9)

 

Knight = N (chess abbr.)

   wearing [insertion]
      Byzantine [anagrind]
         sapphire (charade -> corundum)

      => coundrum

   coNundrum

DEFINITION

mysterious = conundrum

 

Over to you.

quickie:

 

he's got your back fly guy (7)

Copilot....?

wingman…?

 

🪽🤷‍♂️🆘

All yours, countess 

He calculates contributing to Baghdad dereliction. (5)

adder? ++++++++++

Hears......