This is a top five list, with explanation.

5.Onion
Just watch any episode of Steven Universe with his name in the title.

4.Cluster
On every SU fan's heart.

3.Malachite
The actual Malchite stone is highly toxic in water.
Steven gave Connie Rose's sword in case they have to "fight Malachite" (my feels ;_;)

2.Raven Queen(breaking the streak for these two)
Ever since she signed the storybook of legends, she and Apple have been fighting. Over pictures. Raven wants pictures with Chaos.

1.Dipper Pines.
His very name makes you shake in fear... not.(I HAVEN'T SEEN DIPPER AND MABEL VS THE FUTURE YET!)

Anybody remember his breakdown? He pointed a memory gun at his hero and screamed "Trust no one" .
Does Bipper still rest in his mind?

Thanks for calming my fears of everyone but... all of them...