Array element type doesn't match expected

Why: You're feeding an Array<{elem}> into a function that expects Array<{other}>. UE5 doesn't auto-cast array element types element-by-element — you'd lose type safety. Fix: Either: (a) change one array's variable type to match (My Blueprint → variable → Details → Variable Type → set to Array of {other}), or (b) loop over the source array, cast each element individually, and Append to a new typed array. Use the ForEachLoop node for this.

Variable references a deleted or renamed type

Why: The variable '{name}' is typed as something that no longer exists in your project. This happens when you delete or rename a Blueprint, Struct, or Class that other variables referenced — UE5 leaves the reference dangling. Fix: Open the Blueprint that owns '{name}' (in the Errors panel, click the file link). In My Blueprint panel, click '{name}' to select. In Details panel, change Variable Type to a valid type, or delete the variable entirely and remove all references.

Wrong class plugged into a pin expecting a specific type

Why: A pin expected an actor of type '{expected}' (or subclass) but you connected a '{actor}' which doesn't inherit from it. Fix: Either: (a) change your '{actor}' to inherit from '{expected}' by reparenting it (File → Reparent Blueprint), or (b) use a Cast To node to verify the type at runtime, or (c) plug in a different actor that IS a subclass of '{expected}'.

Class

A blueprint or C++ type that can be instantiated. Each spawned Actor or component is an instance of a class.

Interface: implement and call Blueprint interface function

SETUP: Create a Blueprint Interface asset (BPI_Interactable) with a function 'Interact'. IMPLEMENT: In the actor BP, go to Class Settings → Interfaces → Add → BPI_Interactable. Then implement the 'Interact' event that appears in the event graph. CALL: Get actor reference → 'Does Implement Interface(BPI_Interactable)' → Branch → True → 'Interact (Message)' node (the interface call). Key: Interface calls are 'Message' type nodes. Use 'Does Implement Interface' before calling to avoid crashes on actors that don't implement it.

Variable

A named storage slot for a value. Has a type (Boolean/Integer/Float/String/Vector/Object Reference/etc) and a default value.

string

string

Delegate

A type-safe function pointer used by Event Dispatchers and bindings. Bind, broadcast, unbind.

Less (float) — A < B

Struct

A user-defined data type bundling related fields (e.g. S_InventoryItem with Name+Count+Icon). Make/Break nodes convert.