Vladimir matchup: If the vlad is good this is Poppy's worst matchup imo. If he goes ignite you cannot do anything to fight back and he will just w your e then run you down not to mention he can sustain all your poke. Luckily for every poppy matchup the enemy needs to know how to play it and pull it off so if he's bad it's winnable. Ignite can work but I just go spectres early into executioners and look for early trades with e q then try to flash for a wall stun when he's low to finish. If it goes badly rush your hollow asap no executioners and just clear wave best you can taking the least poke possible. He never has to recall so just hold on and hope your ult can make the difference in teamfights.

Cassiopeia matchup: Similar to the Vlad matchup this is super hard for Poppy if Cass is good. Do your best to look for poke on her without getting hit by q. If you get a lead you can take almost any trade and when you get hollow + swiftness boots you can run her down and be a real threat. Otherwise just farm and clear waves best you can.

Mordekaiser matchup: Try to wait for morde to use his spells on the wave then poke with Q. Do not let him hit you isolated with his Q. If you are in a bad spot use e to escape his pull.

Rumble matchup: Play safe early and try to dodge his E poke. Once you get spectres you can sustain most of his poke and farm freely then play for ganks or teamfight.

Garen matchup: Poppy can win the matchup early if you use Q to slow his Q. Do not let him get his full E off on you. If you are struggling get swiftness boots and keep your distance. He makes team fights difficult since he can do 1/3 your hp true damage, negating your W passive and insane tankiness. Play smart and don't get burst down early trying to dive, peel your carries and dont let him get on them.

Fiora matchup: If the Fiora is good this matchup is unplayable. Check early if the Fiora has good reaction time/low ping, if she does you can't use W, E or R without her wasting her W. Just do your best to get XP level 1 without letting her poke you out. If you fall low she can easily finish you with pta ignite burst. Rush bramble and use W only when she is right on top of you so she can't QW it.