What object to cast to

That’s not how casting works Munchito. You have to get a parent class for which your actor derives from. For example, if your Tier1TowerBase is a pawn, you must get the playerpawn through GetPlayerPawn node and link the output to your cast node. If Tier1TowerBase is a character (unlikely if it is a tower but anyway), you must GetPlayerCharacter.

You can find out the base class (or parent class) by opening the blueprint and looking at the top right.

Hope this helps.

I can’t cast between this 2 BPs, what should I have in the object one? Actor Owner doesn’t work (both are actors).