The strategy for extreme is to score as many points as possible during phase 1 by using Hellbram ultimate to strip SBK’s buffs as well as the 2 ads next to him for 20 points per buff removed.
G. Merlin can easily clear out the Dissolve quest while her ultimate can easily burn through Phase 1 if you end up stacking too much time and building too much ultimate orbs on the ads next to SBK.
The Extreme boss only has 292,832 HP so a Jeri Crit will usually overkill the boss allowing you to skip Phase 2 entirely. It may take a bit of RNG but hopefully this will help you secure top 5% 🙂