Hello. This is my Poppy guide. This isn't a full in depth guide but I will explain why poppy and why these items.

Poppy is goat. She is a good tank and has high early game dmg. You can often dive with her if you have a competent jungle. Her w is of the best abilities to outplay people with dashes, and as you know, every new champion has a dash. So poppy is in a good spot here.

Teamfight wise you can do alot by just poking enemies, picking up your shield tank soaking up dmg. If you're extra clever you flank the enemy and stun their carry to take their dmg out of the fight for 2 seconds.

As you see, Poppy is bae.

Since dorans items have been nerfed, corrupting potion has become very viable again. The item gives you everything you need to sustain lane for your first kill. Just be careful when you try to poke near the turret while the potion is active, the turret will focus you due to the burn dmg.

Why Trinity?
Trinity is basically a subtitute to divine sunderer. It gives you everything you need: AD, attack speed, movement speed and haste. This is good because poppy has high dmg in early game and this item fits perfectly for her laning phase. If you happen to get a kill or 2, your enemy won't have a chance once you have this item. You will also have high dive potential because your q will deal 300-400 dmg if both shocks hit + ult knock up + AA = 500-600 dmg in a dive.

With sunfire first you won't get near these numbers. Buy trinity!

Jaksho
Somewhat better now, it gives 30% (!!!) more armor and mr. It scales with runes and your w passive. Just buy it.

Sunfire and boots are pretty standard and haven't changed much. Buy them too!

Try to be aggressive in lane if you are playing against a fighter. A riven, yone or whatever dash happy champ you face won't have a chance against you. Always space and look for openings. If they happen to think they can burst you, press w, hit q, throw a shield into their face and move away. Do this 2 times and you can almost dive them. Kill them if you can.

If your jungle is going for mr.krabs top side, help him/her out and if you're lucky there will be a small tf which often you win if you hit your e.

After early go into mid and help your team at dragon. If a fight happens there, use tp to get there asap. Win tf.

In Late Game you have to be a bit more careful. Any mistake can lead to a stun lock and burst from 5k to 0. Poppy job in late game fights is to stall out the carries by stunning/flanking and soaking up as much dmg as possible. Unfortunately in late game poppy is quite weak compared to other tanks, so try to not get into this state if you can. If you help your team in mid game enough you won't ever reach this state of the game.