The tag implication #70319 synth_(vader-san) -> machine is pending approval.
Reason: Synth are synthetic beings made with mechanical parts. I'm pretty sure they could fit under the definition of a machine.
Topic: Tag implication: synth_(vader-san) -> machine
Posted under Tag Alias and Implication Suggestions
It was already discussed and rejected both for machine and robot in the past:
https://e621.net/forum_topics/33504
https://e621.net/forum_topics/30355
https://e621.net/forum_topics/28666
I personally agree that they should imply the tags robot or machine, but some people don't... Which is weird since even protogen imply machine, and they are more fleshy than synths.