2023-02-04 : A Phyrexian mana symbol contributes 1 toward the mana value of a card, even if life is paid for it. Specifically, Jace's mana value is always 4.

2023-02-04 : Jace's second loyalty ability doesn't care which player's graveyard has twenty or more cards in it. It could be the target player's or another player's.

2023-02-04 : Other replacement effects that would change the number of loyalty counters Jace enters with will apply as normal.

2023-02-04 : 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.