Poppy Jungle: she is a great counter pick for any champ that dashes onto you as an engage such as Rengar. She actually has a decent clear compared to other off-meta junglers. Assassin Poppy is a viable early to mid game choice if at least 3 of the opponents are squishy. otherwise i would build her as a bruiser for a better mid to late game. your damage output is still great and you have much better teamfight potential.

Poppy top: I would almost always build bruiser in top lane matchups unless you are in a tank matchup in which case you might go the conventional poppy build.

Poppy Mid: Poppy is good against other assassins because of her natural robustness paired with her damage output from builder her lethality items. In AP matchups its good to start with a hexdrinker and then build into a Duskblade. This also works better if. you jungler is trundle as he can place a nice pillar allowing you to hit your E.

Poppy ADC/Support: This strategy is very viable in lower elos as most have never played against it and usually fall victim to its deadliness. I would only reccomned doing this if your ADC/Support is Anivia, Veigar, Trundle, or Yorick. Anivia being the best option.