It stacks with Trousseau ;)

Trousseau doesn't work on Zombie Rairyuu and Howlet, this card does.

Trousseau works on any attack or skill that damage scales its damage from the magic stat. So yes, it works on ZRaiyuu and Howlett.

This is not true. All Runeblade skills except for Drain Evocation are Slash attacks that benefit from Slash Up, and do not benefit from Magic Attack Up. Drain Evocation is Magic attack and will be the only skill that benefits from Trousseau's party bonus.

VC do not stack only equipments.. VC with lower stats will be ignored

Trosseau and Blossom in the Dark stacks.
it's Magic Atk Up and Man Eater on Magic Atk.
so Drain Evocation will get boosted by both cards, while Hazard Spell doesn't get boosted by any of them.