Wander:

• the name of his main fairytale is spelled out at the start - 'go I know not whither and fetch I know not what'
• pikefish is from 'Upon pike's will, upon my wish' - I chose this translation because 'at the pike's behest and at my desire' didn't vibe with me
• the Simeons are from 'Seven Simeons'
• the flying ship is more inspired by the old 20 minute animation than its own fairytale

 Basilisk:

• his whole deal is being Vasilisa the Beautiful, though from the fairytale of the same name it's mostly Baba Yaga in the forest and the skull flashlight
• the apples of youth crop up everywhere in fairytales as far as my reading experience goes, so no particular reference point
• Zmei Gorynich, the dragon, is also more of a concept than anything specific
• the yellow ball is a reference. this one is a secret

Valerian:

• his main fairytale is Frog Princess, not to be confused with Frog Prince
• the black cat references classical literature
• the whole Copper Mountain segment is based on Bazhov's tales, specifically Stone Flower and Fire Fairy
• Koschei is there in adherence to frog princess, but the boiling milk thing is actually from The Little Humpbacked Horse

the princes' headwear in the wedding cgs are references to animation - Wander's to the Little Humpbacked Horse, Basilisk's to the Plasticine Crow and Valerian's to the Frog Princess, but I think if I get to redrawing those I should probably switch them around prioritizing color coding