The Giant Sea Snake is encountered at the end of the Royal Trouble quest. It is not as strong as its combat level suggests, but an antipoison potion, preferably super, is vital, as the snake is poisonous with damage that starts at 9. It fights with melee up close and ranged from a distance, but it cannot detect the use of prayers. Like its offspring, it is vulnerable to Magic. It drops the heavy box which is needed to finish the quest, and it can only be fought once.
Level 40 Slayer is required to kill this creature.
The best way to defeat the snake is to attack it up close with magic to exploit its weakness. This way, it will not use its ranged attack, so players can freely use Protect from Melee to reduce the majority of the damage. Other factors such as what food to bring and what armour and weapon to use are left to the player's decision. It is recommended to bring at least lobsters or swordfish. A dwarf multicannon can be setup in this area.
Item Quantity Rarity GE market price Watermelon seed 1 Uncommon 115 Poison ivy seed 1 Uncommon 15 Guam seed 1 Uncommon 9 Marrentill seed 1 Uncommon 6 Tarromin seed 1 Uncommon 6 Harralander seed 1 Uncommon 18 Toadflax seed 1 Uncommon 356 Ranarr seed 1 Uncommon 38,516 Irit seed 1 Uncommon 31 Avantoe seed 1 Uncommon 1,229 Kwuarm seed 1 Uncommon 481 Snapdragon seed 1 Uncommon 51,902 Cadantine seed 1 Uncommon 1,635 Lantadyme seed 1 Uncommon 1,683 Dwarf weed seed 1 Uncommon 865 Torstol seed 1 Very rare 49,149
Item Quantity Rarity GE market price Coins 23; 32; 44 Uncommon Not sold Adamant dart tip 2 Uncommon 420 Pearl bolt tips 3 Uncommon 51 Broad arrow 4 Uncommon Not sold Water orb 1 Uncommon 1,357 Water rune 15 Uncommon 75 Mist rune 1 Uncommon 97 Fishing bait 50 Uncommon 200 Raw bass 2 Uncommon 352 Raw lobster 1 Rare 157 Casket 1 Rare 941 Clue scroll (medium) 1 Rare Not sold Long bone 1 Rare (1/400) Not sold Curved bone 1 Very rare (1/5,000) Not sold