If a spell is cast with an alternative cost that includes mana (such as flashback), Vexing Bauble's first ability won't trigger and won't counter that spell. Similarly, if a spell is cast without paying its mana cost, but the player did pay mana for additional costs such as from kicker or from Thorn of Amethyst, Vexing Bauble's first ability won't trigger and won't counter that spell.

Players may cast spells that they know Vexing Bauble will counter. Any abilities that trigger when spells are cast will still trigger and resolve if appropriate, and any effects that count how many spells are cast will still count those spells if appropriate.