Spent almost an hour and got nothing

Be careful with this boss, your attack power can't be too low, otherwise if you drag the third phase for too long, it will instantly kill you. My first attempt took about 30 minutes of chipping away, and then I suddenly died. I thought, 'Okay, maybe my attack power wasn't enough.' So in the second attempt, I strengthened my attack a bit, but I still got instantly killed. Either there's a hidden time limit, or the third phase has a usage limit 😭. I think this mode is quite fun, but you must pay attention to the balance between attack power and health recovery, otherwise you'll waste a lot of time 😭😭😭. (I've decided to refresh for better stats again)