For this pitch, I will be presenting an idea for the basis behind a boss fight that occurs in an alternative Second Age storyline.
This fight will take place in an alternative version of Runescape whereas Seren and Zaros do agree to work together, during the Second Age, to keep mortals safe. With this reunion, they proceeded to make a guardian to keep this world safe from other Gods. This Guardian, named Dominys, succeeded in its goal and kicked all the Young Gods out save for the now awoken Guthix, who creates a sliver in order to bring heroes in from another time to kill the titan.
Dominys is a crystalline titan that uses both Darkness and Light aspects to fight. Basic attacks include frontal cleave, resistance to a certain style, much like the QBD, a debuff that reduces defense, and lastly, spawning a shadow that does minor damage and prevents the boss from taking damage when alive.
Dominys will have 3 distinct phases:
Phase 1: Dominys is stationary and proceeds charging for a devastating attack. To prevent this attack from going off, the team will have to burn the boss down before he is finished with his channel. At the phase's end, Light and Dark zones will appear during the fight. When these zones appear, the team will have to split into two groups and stay apart for the rest of the fight. If an imbalance occurs, people will be randomly selected from one group and dropped into the other, taking significant damage.
Phase 2: After the Boss is burned down, it becomes aspects of its creators: one of Light and one of Dark. The Light Boss will attack primarily via mage/range while its Dark counterpart attacks via melee/mage. When one is 15% less HP than the other, both will receive a damage boost of 20%.
Phase 3: Both Aspects are enraged and begin using ground AoEs. This phase involves movement while keeping the bosses within 15%.
Loot: Lv 90 Tank Armor, A New Lore Book, New Pet, Various Ores/Gems/Jewelry, and Trisk Pieces. Stats TBD.
If this sounds legit, here's my Runelabs Link: