*Why don't you read this handy, updated manual called *Mask's updated lore* that clearly describes glass is not his weakness. It just slows down his corrosion. This corrosion is what you should be worried about. It degrades organic material like flesh until nothing remains, as well as solid concrete walls and glass. Glass will degrade more slowly.* Mask
*Forgot me already? My brother must have weak memory. I have hurt Mask physically. You haven't been able to, Undyne hasn't been able to, sans hasn't, Alphys hasn't. You need something like me. But just remember Hex, where my brother's power ends... *malicious smile* mine begins...* Masque.