Valakut, the Molten Pinnacle's triggered ability has an "intervening 'if' clause." That means (1) the ability won't trigger at all unless, at the time a Mountain enters under your control, you control five or more Mountains other than that new one, and (2) the ability will do nothing if you control fewer than five Mountains other than that new one by the time it resolves
However, it's actually a ticking time bomb that would unleash a monstrous indestructible creature
[card]Restore[/card] [C+]/[F] In a multiplayer game, this can reliably get you a [card]Terramorphic Expanse[/card] or panorama and should be thought of as another [card]Rampant Growth[/card]
In Living Energy, that might mean repeatedly searching out lands thanks to Solemn Simulacrum (a card that just didn't quite make the cut for this list), making Thopters with Pia and Kiran Nalaar, or tons of energy with Aethertide Whale
Mono-black cards like South Wind Avatar can support these strategies, but its most often used in sacrifice strategies with Blood Artist or Zulaport Cutthroat, or with commanders like Vito, Thorn of the Dusk Rose
But TLA has a lot of high-value cards that fare pretty well, so its not good set to open