The compleated ability looks only at whether a player chose to pay 2 life for a Phyrexian mana symbol as they were casting the spell. If a player paid life for some other reason while casting the spell, that will not reduce the number of loyalty counters the planeswalker enters the battlefield with.
A Phyrexian mana symbol contributes 1 toward the mana value of a card, even if life is paid for it. Specifically, Vraska's mana value is always 6.
In most cases, the target of Vraska's last loyalty ability will end up with nine poison counters. However, once you calculate what the difference is, replacement effects can change how many poison counters the player actually gets. For example, if the player controls Melira, the Living Cure, they will end up getting one poison counter if they had eight or fewer to begin with.
Magic: The Gathering · ™ & © Wizards of the Coast · Illus. Scott M. Fischer
Card data via Scryfall. Rarix is fan-made; not endorsed by the rights holders.
The target of Vraska's second loyalty ability will lose any other subtypes and card types it previously had and will be only a Treasure artifact. It will retain any supertypes it had.
Other replacement effects that would change the number of loyalty counters Vraska enters with will apply as normal.
