Jetmir, Nexus of Revels

Creatures you control get +1/+0 and have vigilance as long as you control three or more creatures.
Creatures you control also get +1/+0 and have trample as long as you control six or more creatures.
Creatures you control also get +1/+0 and have double strike as long as you control nine or more creatures.

Streets of New Capenna

Streets of New Capenna Promos

If a creature with double strike loses double strike after dealing damage during the first combat damage step but before dealing damage in the second combat damage step, it will not deal damage during that second combat damage step. Notably, this means that if your ninth creature dies in the first combat damage step, the rest of your creatures won't deal combat damage again unless something else is granting them double strike.