Non-lands feed your goblins with +1/+1 counters, while discarded lands create Treasures for mana, so you build power and ramp at the same time
The key clause here is you have to play those cards during an opponents turn, forcing you to wait to cast most of your spells
Primal Amulet / Primal Wellspring Double-faced cards that transform into a land are one of Ixalan's specialties, and Primal Amulet/Primal Wellspring is among the best of them
Now back to Amonkhet
Cerberus Supply Runners Tanuki Transplanter Tarkir Duneshaper Tesak, Judith's Hellhound Thraben Foulbloods Thraben Purebloods Thrashing Mossdog Trade Route Envoy Traveling Botanist Trusty Retriever Two-Headed Cerberus Underworld Cerberus Underworld Rage-Hound Vampire Hounds Warclamp Mastiff Wary Watchdog Watchdog Wild Dogs Wild Mongrel
Doctor Doom allows Connive to benefit you no matter the outcome: when you discard a land card, each opponent takes 2 damage, and if it's a nonland card, you still place a +1/+1 counter on the creature that Connived