You should play the card whenever the proliferate effect alone makes sense since you get something extra
I fully realize I left out lots of folks favorites but I sure would like to know them, so please make sure you head on over to Twitter to tell me which Plains you like best and share an image of the art
Drapion V is my favourite and I have been looking for Yuka Morri sketches
Retailers like TCGplayer, Card Kingdom, or even Amazon tend to list these special versions under the cards name, so you can search for something like Doubling Season anime art or Smothering Tithe anime version and see whats available

Dynamite Dark Contract with the Eternal Darkness Destruction of Destiny Dimensional Barrier Discord Dogmatika Punishment Extinction on Schedule Forbidden Apocrypha Gozen Match Grave of the Super Ancient Organism Grisaille Prison Kozakys Self-Destruct Button Lose 1 Turn Macro Cosmos Mischief of the Gnomes Ojama Duo Ojama Trio Phantasm Spiral Battle Pinpoint Dash Relay Soul Ring of Destruction Rivalry of Warlords Secret Barrel Secret Blast Skill Drain Spright Double Cross Stygian Dirge Summon Limit Tearlaments Cryme Tearlaments Metanoise Tearlaments Sulliek The Monarchs Erupt There Can Be Only One Warning Point Welcome Labrynth Limited: Crimson Nova the Dark Cubic Lord Flower Cardian Willow Machina Citadel Swordsoul of Mo Ye Therion King Regulus Trickstar Candina Trickstar Lycoris Virtual World Mai-Hime Lulu Wisdom-Eye Magician Witchcrafter Schmietta Black-Winged Assault Dragon Black Feather Whirlwind Black Whirlwind Lair of Darkness Necrovalley Spell Power Mastery Speedroid Scratch Speedroid Wheel

Among the more important cards to keep in your deck are: Rad Storm Nuclear Fallout Feral Ghoul Hardened Scales Screeching Scorchbeast Best Cards to Add and Which to Swap Out Cutting out cards that lack synergy with the Mutant Menace theme in MTG is necessary for optimal gameplay