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 87 Poison ivy seed 1 Uncommon 19 Guam seed 1 Uncommon 15 Marrentill seed 1 Uncommon 12 Tarromin seed 1 Uncommon 12 Harralander seed 1 Uncommon 33 Toadflax seed 1 Uncommon 1,000 Ranarr seed 1 Uncommon 47,899 Irit seed 1 Uncommon 61 Avantoe seed 1 Uncommon 1,792 Kwuarm seed 1 Uncommon 597 Snapdragon seed 1 Uncommon 60,933 Cadantine seed 1 Uncommon 1,385 Lantadyme seed 1 Uncommon 2,487 Dwarf weed seed 1 Uncommon 402 Torstol seed 1 Very rare 60,225
Item Quantity Rarity GE market price Coins 23; 32; 44 Uncommon Not sold Adamant dart tip 2 Uncommon 404 Pearl bolt tips 3 Uncommon 120 Broad arrow 4 Uncommon Not sold Water orb 1 Uncommon 1,310 Water rune 15 Uncommon 75 Mist rune 1 Uncommon 116 Fishing bait 50 Uncommon 250 Raw bass 2 Uncommon 1,020 Raw lobster 1 Rare 210 Casket 1 Rare 838 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