Endgame Study #29: The Fight for the Diagonal

Hello all! This is the 2nd to last endgame study that will be posted daily .  Read why here. For today's puzzle, I decided to choose a rather funny looking position. Enjoy!

Scroll down for hints...

Small hint: As you're fighting for the diagonal, black might have a "defense" to your idea. Look further! Don't end your variation too soon.

Big hint: You need to stop the a pawn. The title of this post suggests which piece you need to use to do that. Now, the only question is: how?

I hope you guys enjoyed this endgame study! Tomorrow will be the last one, but I will continue analyzing some on my youtube channel if you'd like. Comment down below if you would like me to continue endgame studies on my youtube channel!