Opposites

Opposites are all just two parts of a whole. Without one the other loses it's meaning. If you can control one of them, you'll automatically be able to control the other half. If you could control heat, you can just take the heat away from something and thereby freezing/chilling it.

Without opposites everything would lose it's meaning. If there was no bad what can be considered good? If there was no such thing as death could life or the state of living still be described?

If you ever gain the ability to cultivate, practice magic or whatever, don't limit yourself to something stupid and simple like fire if you could just go for temperature.

A necromancer is pretty much a somewhat successful attempt at combing the powers of life and death since reanimated corpses are technically both alive and dead at the same time.