Similar to acting:
* Pretend like an actor playing a role.
* Mimic a bird's song to attract its attention.
* Masquerade as someone else to gain entry.
Similar to deception:
* Deceive with a fake smile.
* Disguise one's true feelings.
* Conceal one's fear by acting brave.
Similar to faking:
* Counterfeit a signature.
* Forge a document.
* Fabricate a story to avoid trouble.
The best analogy will depend on the specific context in which you are using "feign."