For example, Final Showdown's mana value is always 1, even if you chose all three modes
You don't need to have cast it originally
The rules say that when you resolve a planeswalker, say Jace, the Mind Sculptor, you put 3 loyalty counters on it as it enters play

Advanced Search Sets Random Syntax Abhorrent Oculus Abyssal Harvester Adorned Crocodile Aegis Sculptor Agatha's Soul Cauldron Agent of Kotis Alchemist's Assistant Ambush Wolf Analyze the Pollen Ancient Vendetta Angel of Finality Annie Flash, the Veteran Antiquities on the Loose Aquatic Alchemist Arala, Hedron Scaler Arashin Sunshield Archenemy's Charm Archmage's Newt Ardyn, the Usurper Ascendant Dustspeaker Auron's Inspiration Azula, Cunning Usurper Baron Helmut Zemo Beetle, Legacy Criminal Behind the Mask Bite Down on Crime Boiling Rock Rioter Bonebind Orator Break Down the Door Bulk Up Buried Treasure Bushy Bodyguard Call the Mountain Chocobo Camellia, the Seedmiser Cease // Desist Cease // Desist Champion of Dusan Channeled Dragonfire Clay-Fired Bricks Coalstoke Gearhulk Codecracker Hound Colossal Rattlewurm Combustion Technique Conspiracy Unraveler Constrictor Sage Consuming Ashes Corpseberry Cultivator Crimestopper Sprite Cryptex Curious Forager Cursecloth Wrappings Damage Control Crew Daring Waverider Data Scrubber Dauntless Scrapbot Dawnhand Dissident Daydream Deadly Cover-Up Demonic Ruckus Dig Site Inventory Digsite Conservator Dire Flail Disruptor Wanderglyph Divergent Equation Doc Aurlock, Grizzled Genius Dreams of Laguna Dryad Militant Duel Tactics Earthrumbler Electroduplicate Elixir Emeritus of Ideation

Since it only costs one colorless energy you can wait a few turns until you build up a few more energies to attack with the Lost Dive attack
It cannot resurrect a creature that has already been destroyed