Melira, the Living Cure

If you would get one or more poison counters, instead you get one poison counter and you can't get additional poison counters this turn.
Exile Melira, the Living Cure: Choose another target creature or artifact. When it's put into a graveyard this turn, return that card to the battlefield under its owner's control.

Phyrexia: All Will Be One Promos

Phyrexia: All Will Be One

Melira's first ability creates a replacement effect. If another replacement effect would also change the number of poison counters a player receives, such as that of Vorinclex, Monstrous Raider, the player receiving the counters chooses which one to apply first, regardless of who controls what permanents. This will usually result in that player choosing to apply Melira's effect last and receive one counter. However, if they want to, they could apply Melira's replacement effect first and receive more counters.

Once Melira's replacement effect has been applied in a turn, additional events that would put poison counters on a player don't happen, regardless of any other replacement effects involved.