Methods for forming airfoil, cores for forming airfoil, and airfoils for gas turbine engines are described. The methods include forming an airfoil body about a core assembly, the core assembly comprising at least one core structure having a radially extending purge slot protrusion extending from a portion of the at least one core structure, removing the core assembly from the airfoil body to form one or more internal cavities, wherein at least one internal cavity has a cavity extension define by the purge slot protrusion, and forming a squealer pocket in a tip of the formed airfoil body, wherein a cavity purge slot is formed at the cavity extension to fluidly connect the respect internal cavity with the squealer pocket. The radially extending protrusion has a radial height that is equal to or less than five times a width thereof.