This is a creative idea, but it has balancing issues. It would make things like super combat, bastion, ranging pots etc redundant.
#Raids 4 megarare: Fragment of Jas
quartz blaze
raven bramble
I don't think it would tbh, sure they would have to really think about how much stats it gives and the cooldown, but it is a mega rare, the price of the item would be insane like the others and not everyone will have it making pots still super relevant. I was thinking the effect would only last a few ticks like maybe 16 ticks and have a 20 minute cooldown. So you would have very short bursts of super powerfull attacks and defense on a long cool down. Forcing you to think on when to use it, either for a burst of DPS or to tank a specific hard hitting attack.
river onyx
Ah yes a mega rare that I can use for 3 swings of my scythe every 20 minuets beautiful