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 80 Poison ivy seed 1 Uncommon 23 Guam seed 1 Uncommon 16 Marrentill seed 1 Uncommon 11 Tarromin seed 1 Uncommon 14 Harralander seed 1 Uncommon 26 Toadflax seed 1 Uncommon 904 Ranarr seed 1 Uncommon 50,936 Irit seed 1 Uncommon 43 Avantoe seed 1 Uncommon 1,760 Kwuarm seed 1 Uncommon 452 Snapdragon seed 1 Uncommon 68,123 Cadantine seed 1 Uncommon 1,508 Lantadyme seed 1 Uncommon 2,622 Dwarf weed seed 1 Uncommon 728 Torstol seed 1 Very rare 53,499
Item Quantity Rarity GE market price Coins 23; 32; 44 Uncommon Not sold Adamant dart tip 2 Uncommon 396 Pearl bolt tips 3 Uncommon 93 Broad arrow 4 Uncommon Not sold Water orb 1 Uncommon 1,384 Water rune 15 Uncommon 75 Mist rune 1 Uncommon 93 Fishing bait 50 Uncommon 200 Raw bass 2 Uncommon 678 Raw lobster 1 Rare 134 Casket 1 Rare 676 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