Blood temperature
Version 0.18: This article may not be up to date for the latest stable release of Crawl.
Blood temperature is a trait of all monsters which have blood (most natural, non-insect, -arachnid, -jelly, or -eyeball monsters). Cold-blooded creatures are slowed if hit by a cold attack and are slowed twice as long by Metabolic Englaciation.
Notably Hydras are cold-blooded monster, so if you don't have a slicing flaming weapon to deal with them, another good strategy is using a non-slicing cold weapon to slow them.
For the late game, [Draconian]s which are populating the Realm of [Zot] are also cold-blooded.