It's a very difficult fight, here are some pointers just from my own perspective (have done with no spirit with both Katana and Colossal Greatsword) plus some extrapolation.
Assuming you mean Malenia; (too many M bosses and names Miyazaki lol) To start, you may have to consider saving the mimic for the second phase, because as you said it is almost guaranteed to die either just throughout the first phase, or on the phase transition. Otherwise as far as equipment goes, bleed and frost both work well, and do wonders to tip the kill speed in your favour.
As far as getting through the first phase as a general rule, you need to be able to mix between being aggressive and waiting out her own aggression. Going it solo there are only a few attacks you really need to look for specifically if you take it slow.
The first and most frequent is her normal multi-slash, and there are two versions, one where the hilt flashes, and one where it doesn't. For both versions you will want to roll forward+right, delay a bit then roll forward+left. Both versions have a guaranteed follow-up at different timings, the non flashing version being slower. The non flash version gives you a guaranteed punish, while the flashing version has variable follow-ups, so you need to wait it out.
The second will affect how you approach being aggressive, that being an attack where she dodges and attacks in one motion. This will mostly limit your non punish attacks to one or two R1s depending on your weapon. Not hard to dodge (just roll away from her) but affects how much you can do during aggression windows.
The third and scariest (at least visually and damage-wise), although least frequent by quite a margin is her waterfowl dance. Easy to see coming with her jumping into the air for a few seconds, but takes some practise to dodge. If you are playing from range this attack is seemingly more common, but also seemingly much easier to avoid without changing much, however at melee range you will want a shield with 100% Phys Block, and the Barricade Shield Ash of War or high Guard Boost+Endurance. The first set of slashes will act as a gap closer at range but will miss as long as you move as far from her as you can during the startup, at melee it is extremely difficult to completely dodge, and for consistency sake it's best to just shield it. After that the rest is easy, although maybe a bit unintuitive. The second set can be avoided by rolling straight at her just before it starts, and the third set can avoided by walking towards her and to the right for a second then stopping.
Everything else in the first phase I think is fairly intuitive but of course still punishing.
The second phase is pretty similar with some new stuff, but with a fresh mimic tear, should be relatively easy to get through.
It will still take a while to fine tune the timings, and get accustomed to recognizing everything, but this can get you through the first phase consistently, then all you have to do is dodge the transition attack, mimic up and finish it.
As far as getting through the first phase as a general rule, you need to be able to mix between being aggressive and waiting out her own aggression. Going it solo there are only a few attacks you really need to look for specifically if you take it slow.
The first and most frequent is her normal multi-slash, and there are two versions, one where the hilt flashes, and one where it doesn't. For both versions you will want to roll forward+right, delay a bit then roll forward+left. Both versions have a guaranteed follow-up at different timings, the non flashing version being slower. The non flash version gives you a guaranteed punish, while the flashing version has variable follow-ups, so you need to wait it out.
The second will affect how you approach being aggressive, that being an attack where she dodges and attacks in one motion. This will mostly limit your non punish attacks to one or two R1s depending on your weapon. Not hard to dodge (just roll away from her) but affects how much you can do during aggression windows.
The third and scariest (at least visually and damage-wise), although least frequent by quite a margin is her waterfowl dance. Easy to see coming with her jumping into the air for a few seconds, but takes some practise to dodge. If you are playing from range this attack is seemingly more common, but also seemingly much easier to avoid without changing much, however at melee range you will want a shield with 100% Phys Block, and the Barricade Shield Ash of War or high Guard Boost+Endurance. The first set of slashes will act as a gap closer at range but will miss as long as you move as far from her as you can during the startup, at melee it is extremely difficult to completely dodge, and for consistency sake it's best to just shield it. After that the rest is easy, although maybe a bit unintuitive. The second set can be avoided by rolling straight at her just before it starts, and the third set can avoided by walking towards her and to the right for a second then stopping.
Everything else in the first phase I think is fairly intuitive but of course still punishing.
The second phase is pretty similar with some new stuff, but with a fresh mimic tear, should be relatively easy to get through.
It will still take a while to fine tune the timings, and get accustomed to recognizing everything, but this can get you through the first phase consistently, then all you have to do is dodge the transition attack, mimic up and finish it.
