This is currently just a concept, changes or ditching this idea entirely are possible.

Four times a day (more if there is demand for it), a safe, single way, free for all Clan War will run. The top x winners can be awarded prizes, such as coins, blood money, etc.

Once you enter, your skill levels will change. This will depend entirely on what the game has selected. Hitpoints selected will be a number between half your highest level, and up to 50% higher than your highest level.
For example, the current game running might assign all players the levels:
Attack: 10
Strength: 80
Ranged: 60
Magic: 90
Defence: 30
Prayer: 45
Hitpoints: 75

You will generally be able to use whatever equipment you have as long as it meets the level restrictions. Upon killing a player, you have a chance at obtaining some of the Last Man Standing items to continue on with the war, that will be removed after leaving the war. These items include food, potions, elder maul, dragon claws, etc. Killing a player will always give you food.

Any of the Clan Wars options can get randomly selected. These include combat style restrictions, overheads, special attacks, and F2P only. The map can either always be a specific map or it can be randomly selected from the available maps.

To motivate people to play without giving out insane rewards, something some as a rainbow partyhat could be a rare prize.