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 71 Poison ivy seed 1 Uncommon 18 Guam seed 1 Uncommon 9 Marrentill seed 1 Uncommon 5 Tarromin seed 1 Uncommon 10 Harralander seed 1 Uncommon 31 Toadflax seed 1 Uncommon 795 Ranarr seed 1 Uncommon 45,466 Irit seed 1 Uncommon 47 Avantoe seed 1 Uncommon 1,675 Kwuarm seed 1 Uncommon 379 Snapdragon seed 1 Uncommon 54,551 Cadantine seed 1 Uncommon 1,034 Lantadyme seed 1 Uncommon 2,358 Dwarf weed seed 1 Uncommon 423 Torstol seed 1 Very rare 58,385
Item Quantity Rarity GE market price Coins 23; 32; 44 Uncommon Not sold Adamant dart tip 2 Uncommon 394 Pearl bolt tips 3 Uncommon 120 Broad arrow 4 Uncommon Not sold Water orb 1 Uncommon 1,309 Water rune 15 Uncommon 60 Mist rune 1 Uncommon 162 Fishing bait 50 Uncommon 200 Raw bass 2 Uncommon 914 Raw lobster 1 Rare 210 Casket 1 Rare 731 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