The Summit of the Null Moon was a gathering of planeswalkers on the Null Moon towards the end of the Ice Age of Dominaria. These 'walkers met to discuss how to end the Shard of the Twelve Worlds that locked them in a small fraction of the multiverse.
Although most people present were told that they would find a way to puncture the Shard together, Faralyn, Tevesh Szat and Leshrac had already made their own plans: they would manipulate the present planeswalkers into attacking one another, hoping that one of them would die so they could use their energy to escape the Shard to the plane of Shandalar.
No planeswalker died, but the Elder Dragon Chromium Rhuell and Faralyn's Spellsquire Ravidel did, which apparently released enough energy for Faralyn and Leshrac to escape. Ravidel was resurrected by Kristina and Taysir, but was furious that they saved him instead of his friend Rhuell, went insane and vowed vengeance.
Although the Summit failed in ending the Shard, it did lead to Freyalise and Kristina deciding to cast the World Spell that ended both the time of the Shard and the Ice Age.