Weird Block is a trinket in Damnation, a mod for The Binding of Isaac.

While held, permanently inflict Poison, Weakness, Confusion to all enemies.

Upon entering new floor with this trinket, Isaac will permanently suffer from radiation sickness: Upon clearing a room, 50% chance to add 1 broken heart.

This block is actually Uranium.
The External Item Description for this trinket was hidden. One of the reason is to reference some incident that some people picked up the radiative block without knowing what it is, and brought it home, causing massive damage to themselves, their families, and the neighbour.
Another reason is that the creator think the effect of this trinket is quite obvious.

• Download Damnation from the Steam Workshop.