Giant rock crab

Giant Rock Crabs are massive versions of the much weaker rock crab. They lie in wait for prey, disguised as large boulders. When neared, they attack. They can be found:
 * In the Waterbirth Island Dungeon, or
 * In the Chaos Tunnels (The middle south rift just east of Mage of Zamorak leads directly to them).

Giant Rock Crabs are very strong and extremely resistant to melee and ranged attacks, and thus are only effectively killed using Magic, Also Veracs barrows armour is quite effictive with its unique set effect that can hit through the tough rock-hard armour this method is advised to those with low magic but high melee. Their ability to drop 10 charms at once makes them an excellent way to gather the charms necessary for summoning.

100% drop

 * Bones

Runes

 * 8,16, or 24 water runes
 * 8,16, or 24 earth runes
 * Nature talisman
 * Air talisman
 * Mind talisman
 * Fire talisman
 * Cosmic talisman
 * Body talisman
 * Water talisman

Weapons and Armour

 * Steel platebody
 * Black claws
 * Black warhammer
 * Black platebody
 * Mithril axe
 * Adamant longsword
 * Adamant warhammer
 * Rockshell gloves
 * Rockshell boots
 * Rockshell splinter
 * Rockshell chunk
 * Rockshell shard

Charms

 * 10 Gold charms
 * 10 Green charms
 * 10 Crimson charms
 * 10 Blue charms
 * This monster drops the most amount of charms in Runescape

Seeds

 * Poison ivy seed
 * Herb seed

Other

 * 27 or 137 coins
 * Uncut gems
 * Herb
 * Raw lobster
 * Raw bass
 * Casket (very rare)
 * Tinderbox
 * Level 2 Clue