Magnetron and microwave
Unfortunately, it is possible to make the magnetron work outside the oven, but as the comments have said, this is a really bad idea. Do not fire up a magnetron after removing it from an oven.

You recall what a microwave oven is designed to do? Heat food! Do you know what you are? A big bag of food. 

If you are lucky, you might discover this with your hand. The skin has nerves, and a cooling blood supply, and you'd probably spot it warming long before the proteins begin to denature. If you are unlucky, you might discover this with your eye. The cornea has no nerves and no blood supply, and you'd probably spot it first with your vision going cloudy, as it does exactly what egg white does when you heat it. This would be permanent.

In terms of life-changing injuries, it's even more dumb than messing with lasers without goggles. Do not fire up a magnetron after removing it from an oven.

It's quite easy to take a magnetron apart with a screwdriver and a pair of cutters to release the two ferrite magnets. These are strong enough to be fun, without the bone-crushing danger of neodymiums, but they can still give a fold of skin a nasty nip, so keep them away from 8 year olds (sorry my daughter!)

Before you power up anything removed from the microwave, let me review different sources of high voltage, and the effects of their limited current or energy on the human body.

TV flyback - very limited current, painful shock
TV tube, charged - very limited energy, painful shock
Auto ignition coil - very limited energy, painful shock
Neon sign transformer - fairly limited low current, serious shock, but probably survive
Microwave oven transformer - high enough voltage to jump through clothes, currents to one amp, serious shock, probably die