Despite Tristram’s wall of permission, there’s exactly one card in your hand that he can’t counter: Meddling Mage. Normally that’s not too big a deal, but in this case, you can maneuver the Mage so that Tristram can’t do a thing about your actions. You can’t bring him down to zero life when he’s at his current life total, but you can outmatch him in terms of life total.

That said, the other thing you need to do is figure out how to get Celestial Convergence to trigger before the start of your next turn. You can gain as much life as you want, yes, but it won’t mean much when Tristram can just blow up the Convergence via his Soltari Visionary on his attack.

1. Tap a plains to add , and an island to add (used as generic mana) to your mana pool.
2. Spend to activate Calciform Pools’ ability, tapping it and removing all storage counters to add (three used as generic mana) and (three used as generic mana) to your mana pool. (You now have in your mana pool.)
3. Spend to cast Meddling Mage. When Meddling Mage enters the battlefield, name Disdainful Stroke.
4. Spend to cast Delusions of Mediocrity. You gain 10 life. You are now at 12 life.
5. Spend to cast Restoration Angel. When the Angel enters the battlefield, choose to exile Meddling Mage and return it to the battlefield under your control.
6. When Meddling Mage enters the battlefield, name Dispel.
7. Spend to cast Swift Justice on Azorius Herald. Azorius Herald is now a 3/1 creature with first strike and lifelink.
8. Declare the start of your combat phase, assigning Azorius Herald to attack.
9. Because Azorius Herald is your only attacking creature, Guardians of Akrasa’s Exalted ability triggers, giving the Herald +1/+1 until end of turn. Azorius Herald is now a 4/2 creature.
10. Because Azorius Herald can’t be blocked, it deals 4 damage to Tristram. Tristram is now at 19 life.
11. You gain 4 life due to the Herald’s lifelink ability. You are now at 16 life.
12. At the start of your second main phase, tap two plains to add (both used as generic mana), two islands to add , and Azorius Chancery to add (both used as generic mana) to your mana pool.
13. Spend to cast Ghostly Flicker, targeting Meddling Mage and Azorius Herald, exiling both creatures and returning them to the battlefield under your control.
14. When Azorius Herald enters the battlefield, you gain 4 life. You are now at 20 life.
15. When Meddling Mage enters the battlefield, name Outwit.
16. Spend to cast Donate, giving Tristram control of your Celestial Convergence.
17. Declare the end of your turn.
18. At the beginning of Tristram’s upkeep, Tristram must remove the last omen counter on Celestial Convergence. At this point, you are at 20 life against Tristram’s 19 life, and you win the game.