Ridiculous superhero weaknesses

[Mat001]

Kryptonite. It is a massive cultural reference but explanation of how some radioactive element renders Superman's god like abilities impotent makes no sense whatsoever. But to be honest, the explanation of the yellow sun giving him the powers is equally crazy so I guess there is a symmetry there.

Yellow sunlight is absorbed in the body of a Kryptonian, resulting in the granting of powers. A result of genetic tampering. Kryptonite radiation causes a reverse photosynthesis which results in a Kryptonian losing their powers and dying from the intense radiation.

Mr. Mxyzptlk from Superman created his own weakness, and that is saying his name backwards

That's not a weakness. That's the rules of the game. Mxy thought that he could outsmart Superman and this was the result of the name game.

[robowizard]

golden age Green Lantern being vulnerable to wood and current Green Lantern being vulnerable to the color yellow

[dupersuper]

Well the mechanism for Zatanna's magic is based entirely around speaking. If she could cast spells with gesture then what would be the point of saying things backwards all the time?

It's a focusing help, not needed.

Superman not being able to see through lead. There are plenty of stuff around with equal density, and why would just one of his god-like powers have such an arbitrary limit?

It's not just lead: he's had trouble seeing through other extremely dense material. That's how x-rays work.

golden age Green Lantern being vulnerable to wood and current Green Lantern being vulnerable to the color yellow

Only rookie Lanterns currently have trouble with yellow.