My idea would be to add 2 new slayer bosses, but with a catch. The bosses would have reduced damage from lower modes than elite.
Elite would do normal damage.
Classic mode would do -15% damage.
Extreme mode would do -30% damage.
Normal mode would do -45% damage.
ofcourse the damage could be raised with slayer items like slayer armor, slayer helm(i) etc.
First boss: Helwyr, cost 5000 blood money to enter.
Who drops the Wand of the Cywir elders 1:750
Wand gives 15% damage boost on slayer tasks and requires no runes to use.
To enter the next boss you need to combine an ancient sigil from Seren, Sliske, Zamorak and Zaros sigil pieces that Helwyr drops. 1:250 each, cant get 2 of the same sigil pieces.
Second boss: Telos, the Warden, cost 10,000 blood money to enter
Group boss who drops Seren godbow, Staff of Sliske and Zaros godsword. When you get a drop their uncharged. 1:999
ALSO has a chance to drop all the bloodmoney paid for enterance fees as a jackpot 1:1800 jackpot goes to 0 and starts building again from enterance fees when its won.
To charge the weapons you need to have
x1 Orb of corrupted anima 1:250
x1 Orb of pure anima 1:250
x1 Orb of valcanic anima 1:250
To charge the weapons you also need 99 crafting what makes the weapon also untradable after charging.
All of these weapons give 25% damage boost on slayer tasks, 1:16 chance to berserk and 1:16 chance to heal you for 50% damage dealt.
Bow requires 99 range to wear.
Staff requires 99 mage to wear.
Godsword requires 99 attack to wear.
IF you got 200m exp in any of these skills only on x2 exp then the weapon powers are doubled - 50% damage boost on slayer tasks, 1:8 chance to berserk and 1:8 chance to heal you for 50% damage dealt. Elites must use 200m cape on weapon to upgrade it.
I think this would motivate players more to create an additional account on x2 if they havent already. And why not better prizes for people who work harder on their goals.