Giant rock crab

Giant Rock Crabs are massive versions of the weaker Rock crab. They lie in wait for prey, disguised as large boulders. When approached, they attack, unless they have become tolerant, in which case they remain as "boulders" - attempting to cast a spell on them gives the message "You can't attack this NPC."

Locations
In the Chaos Tunnels (The middle south rift just east of Mage of Zamorak (Abyss) leads directly to them). This is recommended when not having a companion)
 * In Waterbirth Island Dungeon (to enter you require a partner)
 * Jagex commented about a future update on January 11th 2012 that the Giant rock crab will have a stronger rival and will become a new slayer monster assigned by Kuradel. It will be released in Kuradel's Dungeon.

Strategy
Giant Rock Crabs are extremely resistant to Melee and Ranged attacks, and thus are only effectively killed using Magic. However, Verac's armour and Diamond bolts (e) are quite effective with their shared unique effect, which can hit through their high physical and ranged defense, Verac's armour also has a prayer bonus allowing the player to use Protect from melee for longer than usual. This method is advised for those with a low Magic level but high melee combat levels. For lower attack levels the use of Attack Potions can be used to improve the chances of hitting. Rock Crabs drop three charms at once, and are a very good source of gold charms. These Crabs are not immune to poison, but are extremely difficult to poison them with a poisoned weapon like the dragon dagger or any poisoned ranged ammo because of their high Melee and Ranged defense.

Another methods includes wearing rune or better armour, and bringing a weapon with a high crush attack bonus, such as the Zamorakian spear or Barrelchest anchor. Slash weapons such as the Abyssal whip are not recommended due to the crabs' high slash defense.

A notably effective and economic way to kill Giant Rock Crabs is the Black Salamander, or the Polypore Staff. The Black Salamander's magic attack, and the Polypore staff's attack acts as a normal magic attack and takes advantage of their lower magic defense. Their magic defense is so low you can utilize high level defensive armour without losing much accuracy.

Giant rock crabs have a very high defence, but relatively low attack and strength. If attacked in the Chaos Tunnels they will walk off and stop attacking you after a minute or two.

An easy way to mage/range them is to use the Chaos Tunnels entrance north of Varrock. To do this, get your best mage/range armour that you have, and go to the Grand Exchange. North-west of the counters is a small under-wall tunnel. Go through it, then jump over the wilderness wall, and head north along the river until you see a Mage of Zamorak that you can trade with. Head north-east from there till you see a rift with a rope in it. Go through it, and you should see a small area with a lot of boulders. Head to the north-east most part of it, where there should be a portal. North of that is a crab boulder and a few stalagmites. Wake up the crab there and go north of the stalagmites. You should be able, from here, to mage/range to the crab without taking any damage. A great method is using Fire Bolt and Chaos Gauntlets. Wearing Mystic and a decent shield for when they get too close to you (Lunar equipment or Splitbark armour are also acceptable), bringing Excalibur from Merlin's Crystal Quest (or Enhanced excalibur from the hard Seers' Village Tasks) will help otherwise. Using this method you can average a bit above 100 charms and 35k exp per hour while spending under 100k.

If using mage, note that they are most vulnerable to air-based spells.

Mage Gear is as follows: Note: Another useful tactic is to use (Elite) Void knight equiment, preferably with a Deflector and a good mage robe top.
 * Helmet: Farseer helmet > Infinity> Ahrim's > Dagon'hai > Mystic/Sacred clay
 * Necklace: Stream necklace > Amulet of fury > Amulet of glory > Amulet of magic/Amulet of power
 * Cape: God cape > Soul war cape > Ardougne cloak (4/3>2) > Obsidian cape, Cape of Accomplishment,
 * Body: Ahrim's >Infinity> Dagon'hai> Mystic/Sacred clay
 * Legs: Ahrim's >Infinity> Dagon'hai> Mystic/Sacred clay
 * Weapon Slot: Polypore Staff,Elemental staff or a 'Magic damage'-increasing staff
 * Shield: God book (Unholy>Ancient>Balance) or Broodoo Shield > Mage's book > Arcane spirit shield
 * Gloves: Barrows gloves > Rune gloves > Lunar gloves > Regen bracelet
 * Boots: Infinity > Wizard's > Mystic > Lunar > Swanky
 * Ring: Seers' ring (i) > Explorer's ring > Beacon ring > Lunar ring or: Ring of Wealth

If you are using ice burst or barrage the arcane stream necklace is not as important here because magic damage boost adds only to the target you click on. The other 8 targets do not receive the damage boost from it or your staff, so you would be better of using a necklace with a prayer bonus.

(if using burst or barrage) + Staff of light is recommended despite the lower mage bonus (in comparison to Master wand, or Chaotic staff) given the fact that it gives free casts; when used in conjunction with Battle Robes, it has a 50% chance of saving runes when casting, and even when this effect doesn't activate, the Battle Robes themselves have a chance to save runes, effectively adding up to a 60% chance of saving runes. The Battle robes will, however, only last for 6 hours of combat / afterwhich they will need to be recharged (270 tokens).

Provided you are going to be bursting a Tome of frost is recommended above items that provide a higher magic bonus. This is because rock lobsters have fairly low magic defence (thus the difference in offensive magic bonus is negligible), while the tome saves an inventory space and the need/price of Water runes.

Retreat
The Giant Rock Crab is one of few monsters in RuneScape that will retreat from battle when they become critically wounded. One way to avoid this (in the southern room in the chaos tunnels) is to kill the eastern one first (using the safespot in the picture above). Then when picking up the drop from him you will have probably alerted a few other giant rock crabs. Go back to the safespot and two should follow you there, from there kill them. While you're killing them the one you first killed should spawn but not attack (unless you go beside it). Because he spawns the other two can't get out and are trapped, so they cannot retreat. After killing the first one, don't pick up the drop and proceed to kill the 2nd one. This means that you will not alert the one that spawned and you will have another retreat free kill. Do this over and over.

27 May 2009
After the 27 May 2009 update, Giant Rock Crabs drop Charms in groups of three instead of ten. However, charm dropping rate was increased significantly. This hidden update initially angered players, though complaints died down as the rate of dropping them was increased.

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Runes/Talismans

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Weaponry/Armour

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Seeds

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Herbs

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Other

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Rare drop table drops
Giant Rock Crab Giant Rock Crab