The adjective fiendish means cruel, wicked, and evil. It often describes things that are not supposed to be alive, like monsters.
The creature was so fiendish that even the bravest of men was afraid to approach it.
The fiendish witch was able to cast spells that made people sick.
adjective
extremely evil or cruel; expressive of cruelty or befitting hell
Synonyms:
1
I know of your fiendish plans.
2
He transforms into a fiendish demon dragon.
3
This provides the sort of tense and fiendish gameplay.
4
Can they be allowed to continue their fiendish reign of terror
5
He is not a perfidious or barbarous or fantastically fiendish foe.
6
Halloween's fiendish fun translates into big bucks.
7
Most people might not be aware of is his fiendish love.
8
I had been duped by fiendish studio producers.
9
This halloween bash is perfect for inviting your fiendish friends.
10
He then chuckles at seeing the girl's fiendish gleam in her eyes.