I would go with Megalon for this match. Compared to Red King, Megalon has superior agility and weapons, which may be able to overwhelm Red King. Red King is considered to be a strong monster, but he usually picked on weaker monsters and he was brutally killed in a quick match with Ultraman. On both occasions where they fought, Ultraman's weapons were able to make the tide of the battle go into his favor. Red King, despite his so-called strength, would not be able to handle Megalon's weapons too well.
Red King: 3/10