Kozilek, the Great Distortion Kozilek, the Great Distortion introduces a guessing game where players navigate around the potential mana value of cards in the Kozilek players hand
If the creature Rancor would enchant is an illegal target by the time the spell tries to resolve, it doesn't resolve

Abominable Treefolk Adarkar Valkyrie Adarkar Windform Alpine Guide Ascendant Spirit Avalanche Caller Berg Strider Blizzard Specter Blizzard Strix Boreal Centaur Boreal Druid Boreal Griffin Boreal Outrider Centaur Omenreader Chillerpillar Chilling Shade Conifer Wurm Diamond Faerie Draugr Necromancer Frost Augur Frost Raptor Frostpeak Yeti Frostwalla Frostweb Spider Goblin Rimerunner Grim Draugr Gutless Ghoul Hailstorm Valkyrie Ice-Fang Coatl Iceberg Cancrix Icebreaker Kraken Icehide Golem Icehide Troll Isu the Abominable Jorn, God of Winter Karplusan Wolverine Moritte of the Frost Narfi, Betrayer King Ohran Frostfang Ohran Viper Ohran Yeti Phyrexian Ironfoot Phyrexian Snowcrusher Phyrexian Soulgorger Pilfering Hawk Priest of the Haunted Edge Rime Tender Rimebound Dead Rimefeather Owl Rimehorn Aurochs Rimescale Dragon Ronom Serpent Saddled Rimestag Sculptor of Winter Spirit of the Aldergard Squall Drifter Stalking Yeti Svella, Ice Shaper Thermopod Wall of Shards Zombie Musher

It's one of many 'edict creatures' that force players to sacrifice something when they enter the battlefield, and it might be the best version ever printed
This can often leave them with little room for their Kirlia and Gardevoir, which provide draw power throughout the game