"Petals of the Shredding Rose..."

You touch the blade used as the material component and imbue it with magic before stabbing the blade into your opponent. Make a melee weapon attack using that weapon against a creature. On success you have stabbed them and deal the damage for your weapon attack as normal. The target, once stabbed successfully, has the following restrictions applied until the end of your next turn: they cannot use any Legendary Resistance features, cannot use any Legendary Actions, lose all Temporary Hit Points, they cannot take reactions, and have their speed reduced to 0.

"... Bloom...."

While the blade is inside them it increases and uncountable blades instantly manifest out from it, jutting out from the opponent in all directions. The target must make a Constitution saving throw and on failure they receive 10d12 magical piercing damage or half on success.

"... and Scatter!"

As you withdraw the weapon the blades become serrated like razors and as they shrink back into the weapon's blade they twist and turn completely in various directions with great speed to shred the body to pieces. The target must make another Constution saving throw - with disadvantage if they failed the previous one. On failure they receive 10d12 magical slashing damage or half on success. If this damage reduces a target to 0 hit points the body is completely reduced to shredded pieces and the target immediately dies.

All damage dealt as part of this spell be it the effects of the weapon attack or the saving throws, completely bypasses all forms of damage resistance and damage immunity.