You cannot activate “Tailor of the Fickle” selecting “Premature Burial” as a target.
You cannot activate “Fairy’s Hand Mirror” to make your opponent chose a different monster when they activate “Premature Burial”.
If you activate this card and your opponent chains “Imperial Order” the effect of “Premature Burial” is negated and the Special Summon never occurs, but you still pay 800 Life Points. If “Imperial Order” is activated after “Premature Burial” is already on the field, the equipped monster is NOT destroyed and “Premature Burial” remains on the field meaninglessly. If “Premature Burial” is then destroyed while “Imperial Order” is still active, the monster remains on the field, but if the monster is destroyed, “Premature Burial” is also destroyed, since it is still equipped to that monster.
If the equipped monster is flipped face-down “Premature Burial” is destroyed but the monster is not destroyed.
Netrep Rulings:
“Premature Burial” is a targeting effect targeting a card in the Graveyard.
An already active “Premature Burial” is not negated when a “Necrovalley” is newly activated.