Seren is located in the wilderness and you will lose items upon death.

Rewards

Once Seren is defeated a 1-2 Seren Keys and 1-5m GP will be sent to your bank.

Preparation

Since Seren is in the wilderness having quick escape methods from PKers are a must.
One method is to purchase a Royal Seed Pod from the PVM Store for 650 points. Clicking on it will teleport you out of the wilderness below level 30.
Seren has multiple spawn locations around the wilderness, some above level 30. Knowing your way to the nearest teleport obelisk or running through trees can help shake off those pesky pkers.
Use the best range set-up that you're comfortable to potentially lose. This will also increase your magic defence against Seren's magic attacks.
A charged Craw's bow has a damage increase to monsters in the wilderness so this is a good option if you have it.
Depending on gear-set up and combat levels, there's a chance you'll run out of food. So keep enough on you incase you find a pker on your way to the bank.
A gamechat message will show when Seren spawns, along with his location and level of wilderness.

Take 2-3 Super Restores/ Prayer pots, an Overload/ range potion, Royal Seed Pod, and your best food.

The Fight

Seren spawns every 40 minutes, the spawn timer is found in the quest tab/ info tab next to bosses. The left timer is for Seren, the right for Mimic.
Click on the timer to teleport to seren, or type ::wildyboss in the gamechat.
Click on the fragment of seren to begin the fight. Stand back, protect from magic and keep your HP high.