There are 2 types of blood crabs - the ones that live on land and the ones that live underwater.
The ones that live on land usually spawn with other turtles around. The underwater ones also hit slightly harder.
Damage Taken From Elements
Knights should just melee. Paladins should use a one-handed weapon (such as royal spears or enchanted spears) and a shield. Mages should use a wand/rod that does energy or death damage and exori vis. All vocations should avoid getting surrounded.