"My duck is tasty."
Translation:Moja kaczka jest smaczna.
No, it can't, it wouldn't make any sense grammatically.
You can sometimes omit 'jest' in sentences like "This is X" (To jest duży pies vs To duży pies), but it's hard to say when it's perfectly okay and when it sounds strange.
Is grammatically correct to say "To moja smaczna kaczka"? Not in this case, I mean.