"If Mario comes close, Thwomp will try to crush him. Since Thwomp is covered with thorns, Mario can't touch him."-SMB3 Instruction Manual

"A nasty block of blue stone that will try to mash Mario in the Fortresses." - SMB3 Strategy Guide

"A stone with motion sensors, Thwomp crashes to the ground when anything tries to pass beneath him. Wait until he's on his way back up to cross." - Mario Mania

"Thwomp, the ultimate gate-crasher, not to mention floor-basher and Mario-smasher, rudely intrudes on your jaunt through the Vault. If you're on the stairs when Thwomp thumps the floor, you'll tumble back down. Spring up the stairs with bounding jumps to reach the top in one go." - SMRPG Player's Guide

"You can ride on its head, but you don't want to get stomped by this stone." - Super Mario 64 Player's Guide

"Thwomps spend most of their time suspended in mid-air, waiting. When Mario passes below, they crash down on him with amazing speed. As you may guess from their appearance, they're heavy and solid enough to make any attack on them futile. Small ones are called Thwimps: despite their weight, they often form groups and bounce around." - Super Smash Bros. Melee