Items, cards and gems. Nothing new. As far as I understand, you are just about to unlock Milestone, which gives *1000 bone capacity for each level.
I took Ancient Wealth and Ancient Spirit for gems. To develop faster.
In the items Shirt, Campfire for survival Toxic Sword, Forbidden Sword for damage and, of course, Red Staff. Actually, it provides maximum damage :) However, for this you need to use his ability as many times as possible. Three days is catastrophically short, unless you will use a cooldown. If there is a sixth slot Club, it gives a huge plus to the damage, though removing the crit. But you can't collect a crit set at 90 levels.
Cards... I wrote just below. You can already level things up in your 90s, but can you improve anything up to level 5? The 5th level will give you *1.7 to attack-defense. So if you can, buy cards, equip things and upgrade them to the 5th.
And the rest... Nostalgia. More, more heirloom! :) Cryolab. You say one session is three days? So you'll get the same amount in cryolabs. But you will get more profit in the future. And, again, gems. Ancient... everything. Cards. Have you collected all the sets? Treasures. Did you buy all the treasures? Generals. Have you gathered all the generals? School. Did you buy all the books?
In general, there is no special secret. Hit this wall with your forehead. Someday it will break :)
(Update)
Or you can use tactics, the mere mention of which causes unanimous rejection among visitors to this site :) You say your session is 3 days now? Double it! :) During this time, you will gain twice as many bonuses from Red Staff, which will double your attack. This is enough to go one level further. This will increase the capacity of Corrupted Soul by about 30% and their income by almost the same. Play for another day or two and accumulate twice as much Corrupted Soul as usual. Even with a fine. Do the prestige. Now, with the help of cryostasis, you will receive Soul twice as fast. Freeze it for a few days to buy some prestige upgrades. Repeat the procedure :)
This is exactly what I keep saying over and over again :) There is no other tactic except to increase the duration of prestige over and over again. But people tell me to just wait. And the author will fix everything. Absolutely! :) And then, in this bright someday, there will be universal happiness, paradise on earth, and prestige no longer than 1.5 days :)