Cast Realm-Scorcher Hellkite by paying 4 and sacrificing another artifact, enchantment or token.
When Realm-Scorcher Hellkite enters the battlefield, it and Lathliss trigger twice.
Resolve both Realm-Scorcher Hellkite triggers, adding 5.
Resolve both Lathliss triggers, creating two 5/5 Dragon creature tokens.
Activate Temur Sabertooth by paying 1, returning Realm-Scorcher Hellkite to your hand from the battlefield.
Repeat.
This brilliant loop hinges on the mana-generating bargain trigger of Realm-Scorcher Hellkite, which is doubled by Elesh Norn, Mother of Machines to yield eight total mana upon entry—more than enough to fund the entire operation. Lathliss, Dragon Queen takes full advantage of these repeated entries, doubling up thanks to Elesh Norn to flood the board with pairs of 5/5 Dragon tokens every single cycle. Finally, Temur Sabertooth provides the escape hatch, bouncing the Hellkite back to your hand so you can recast it and repeat the explosive sequence indefinitely.