For tall core pins, you cannot drill horizontally. Use a (a vertical plate inside a drilled hole) or a bubbler (a small tube that jets water to the bottom of the pin). If you ignore this, the core pin will overheat, and the plastic will stick.
: Mold walls must be tapered to allow the part to slide out easily. Recommended : 1–2° for outer walls and 2–3° for inner walls. injection mold design guide
To avoid sink marks on the opposite surface, ribs should be 40% to 60% of the nominal wall thickness. For tall core pins, you cannot drill horizontally