Gabriel’s blockers are too big to slip through, so you need to find an alternate means of damage. You don’t have anything in your hand, battlefield or graveyard that can help… but Gabriel certainly does, and your Dimir Doppelganger is the ticket to your sneaking the game out from under his nose.

1. Tap three islands to add , three swamps to add , and Everflowing Chalice to add to your mana pool.
2. Sacrifice Bottle Gnomes to activate its ability. You gain 3 life. You are now at 9 life.
3. Spend to activate Dimir Doppelganger, exiling Bottle Gnomes from your graveyard. Dimir Doppelganger is now a copy of Bottle Gnomes.
4. Tap Coretapper to activate its ability, placing a charge counter on Dimir Doppelganger. (You may do this because the Doppelganger is currently an artifact creature.)
5. Sacrifice Coretapper to activate its ability, placing two charge counters on Dimir Doppelganger. Dimir Doppelganger now has three charge counters on it.
6. Tap Power Conduit to activate its ability, removing a counter from Everflowing Chalice and placing a charge counter on Dimir Doppelganger. Dimir Doppelganger now has four charge counters on it.
7. Spend to activate Dimir Doppelganger, exiling Coretapper from your graveyard. Dimir Doppelganger is now a copy of Coretapper.
8. Tap Dimir Doppelganger to activate its Coretapper ability, placing a charge counter on itself. Dimir Doppelganger now has five charge counters on it.
9. Spend to activate Dimir Doppelganger, exiling Lightning Reaver from Gabriel’s graveyard. Dimir Doppelganger is now a copy of Lightning Reaver.
10. At the beginning of your end step, Dimir Doppelganger’s Lightning Reaver ability triggers, dealing damage equal to the number of charge counters on it to each opponent. Dimir Doppelganger deals 5 damage to Gabriel, defeating him.