[johndallman]

When I saw the thread title, my first thought was "Uncontrollable Appetite".

The simple calculation for a relativistic collision is a Slam, per p. B371. The speed of light is about Move 3.3*10^8, so an impactor does 3,300,000 dice of damage, call it ten million HP, per hit point it has. This probably underestimates the damage.