As you may have thought already we didn't follow any strategy guide, we were with higgls

Instead of any common and sucessfully tested strategies we decided on the fly to totally surprise and confuse Crumena by continuously falling dead, leaving him without any targets (must have died around 25 times at least

If dieing is not your style and "going in and beat the thing" like higgls called his own "strategy" doesn't work (it definitely doesn't with Crumena), here is how to do it the least painful way:
Beware of his flying attacks. Prevent him from taking off by Windmilling him. A Windmill can even bring him down again while he is just starting to take off but it's hard to time. Any Smash attacks (pets included) will most likely make him try to use a flight attack. (Yes, that's why he kept spamming us with these

The best way to prevent him from flying is having some people (or just one with a bigger Windmill radius) spam Windmill on his legs AND tail simultaneously. (each of his legs and his tail work as a stabilizer, making your hits less effective if one of them is not hit). If all of his "stabilizers" are hit, his Heavy Stander might fail. Also he won't be able to attack because he will be busy holding or finding his balance.
At the same time someone should attack his chest or back where they have the best chances to land a good blow. The most guides don't mention that his mouth actually is his weakest point, although it can only be hit when it's open. I noticed that I did land some 700+ Criticals on his mouth getting messages that I might have found his weakest point and having him hurt seriously. Targetting his mouth from that point my hits got repelled by Heavy Stander each time his mouth was shut.
It might be a good idea not to wear any armor at all when you fight Crumena, since it won't protect you effectively against his attacks anyway. You are most likely to die once he attacks you, so if you dont worry about loosing some XP, "revive right here" is the best choice. You can windmill him endlessly if you are in deadly state and it doesn't really matter whether he one-hit-kills you from 1 HP or from 1500 HP. The earlier mentioned strategy of higgls with some slight modifications and coordinations might lead to victory without loosing a single life.
Remember: a true stategist is always ready to recognise and adapt.