Murder/Torture plans
*Usage of simple spells*
Using Wingardium Leviosa to levitate toxins/poisons (or simply muggle weapons) is a simple and hard to track way of murder
Petrificus totalus in combination with Lumos very near to the eyes could blind the victim
*More advanced magic*
If physical shields exist, cast one on yourself in an area where apparition is impossible (i.e. Hogwarts or the disapparition wards DEs are so fond of) and then use Incendio to burn your enemies
Cast Fiendfyre in the middle of a place you want to destroy and stop controlling it
Conjure/vanish things inside of things (conjure metal in someone’s lungs, vanish their blood etc)
Modify canary creams into cockroach creams and your enemy is easily crushed (you can also put said enemy in the house of another one so they can destroy the cockroach and you cannot be found guilty)
Spells that stop electrical activity to cause heart attacks
Magically affecting light:
A spell that causes someone's eyes to become reflective or causes photons to bounce off them. A spell to cast light so concentrated it can burn, or blind. Magic flash grenade
*Animals/creatures*
Basilisks
Someone should’ve made a basilisk to have a sneaky little assassin snake that can be carried around in the pocket after being disillusioned – maybe send it with someone who doesn’t know about it to a place where you’re not