wallbreaker | Arkanoid/Breakout clone written in C and SFML | Game Engine library

I'm a first grader of a software engineering study and I have some trouble with a showcase I have to make. I give you a quick rundown of my project.

I don't know if anyone is familiar with the game Clash Royal? Its a game based on getting higher in trophies and collecting cards. And each arena unlocks new cards.

I want to make a deck builder. Where you can select 8 cards, and I calculate the average elixer cost. I want a function that can display all the cards available for your trophy range.

With that out of the way, let me explain my problem: I made a Superclass: Card, and the classes Troop, Spell, DefBuilding, and PassiveBuilding extend on that superclass. After that, I created a class: CardPool where I defined all the objects for all the "Card classes".

Then I made a Class: Arena, and in my main, I declared all the arenas. The thing I am struggling with is the fact that I don't know how I putt all a few cards in a vector of the matching Arena. Something like card 1-2-3 needs to go into a vector of Arena 1 and card 4-5-6 need to go in a vector Arena 2. Only I have 4 different Classes witch all are cards.

So the actual question is as follow: How can I make a vector list of Arena 1 (or 2,3,4) and put 2 Troops, 1 spell, 1 defBuilding into that vector list? And eventually, be able to display them.

The last ting I tried was to Cast the class as you can see in my CardPool class. That didn't work.

note: I made my Class CardPool an interface just to try things out, heard something on school about it.

Superclass: Card