When Mon-El signals Clark Kent at a seance that the Aurora Borealis is causing a rift in the Phantom Zone just big enough for him to poke his hand through, Superman turns himself
into a Superbaby by Red Kryptonite exposure. After ascertaining the truth of Mon-El's statement by entering and leaving the Zone itself through the hole, he, Supergirl, and Krypto burn up the
Aurora Borealis with their heat vision, and the rift closes. Later, Superman returns to his normal size and age.