so with the stage 3 buff on sonic must die mode, i think i found out a good strategy for it. Right at the start go mighty drive and spamming normal attack (you need all the sp for the end of phase 2). always keep your eye on your heatlh, if it under 3300, you are done because seelkadoom can do 2-3 attack in 1 turn. when your sapphire energy at 100, use hyper drive not using light speed judgment, why? light speed judgment only do around 50000 damage, using hyper drive and then spamming blindside basher with 3-4 time healer, you can do 70000-90000 damage, but you need to time it right, 1 milisecond wrong can go horribly. use hyper drive 2 time will left seelkadoom around 20000-40000 health, that when the sp at the start come in clutch, spamming healer until your sapphire at 100 and go light speed judgment. Took me a couple try to found the good strategy but i think this is the best one