Parent Class

The base class your Blueprint inherits from (e.g. Actor, Pawn, UserWidget). Determines available functions and components.

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}'.

Function name collision with parent class or duplicate

Why: You created a function named '{fn}' that conflicts with one already defined — either by the parent class (which you should Override instead) or another function in this same Blueprint. Fix: If you meant to override a parent function: delete your function, then right-click in My Blueprint → Override Function → pick '{fn}' from the list. If you meant a separate function: rename yours to something unique (e.g. '{fn}_Custom').

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Power — raise base to exponent power

Internal function name is MultiplyMultiply_FloatFloat (operator **).

Overriding a function but didn't call the parent version

Why: When you override a parent function (like BeginPlay or Tick), the parent's logic usually still needs to run. Forgetting to call Parent: <FunctionName> can break initialization. Fix: In your overridden function, right-click in empty space → search for 'Parent: <FunctionName>' (e.g. Parent: BeginPlay). Add that node. Wire it to the exec input early in your function, before your custom logic.

Possess — make a Controller possess a Pawn

Pickup and collectible system with overlap trigger

Pattern: Pickup actor with SphereCollision(overlap), StaticMesh visual. OnComponentBeginOverlap → CastTo PlayerCharacter → Success: call AddScore/AddItem interface on player → PlaySoundAtLocation → SpawnEmitterAtLocation → DestroyActor(self). Set collision to OverlapOnlyPawn for performance.

UserWidget

Parent class for Widget Blueprints. Override Construct, Tick, OnPaint, etc.

Two Blueprints reference each other in a way that can't compile

Why: '{a}' includes '{b}' as a hard reference, AND '{b}' includes '{a}' as a hard reference. UE5 can't compile either one first without the other already being compiled. Fix: Break the cycle by making ONE side use a SOFT reference (TSoftObjectPtr). Pick the side that doesn't need {b} immediately at construction — change the variable type to 'Soft Object Reference' instead of 'Object Reference'. Use Load Asset to resolve it at runtime.