There are some strategies which can encourage a player to fall into the trap, for instance by banishing their glimmers when they are running an ink-heavy sapphire deck
But the card can pull some weight in Equipment-only mode, as the power-toughness buff it provides is decent, especially on a smaller mana value creature
If you can keep him around for a while, he has two different abilities that can turn the tide on your early to mid-game
Truly, it is nothing particularly memorable as a game
To determine the total cost of a spell, start with the mana cost or alternative cost you're paying (such as a flashback cost), add any cost increases (such as kicker costs), then apply any cost reductions (such as that of The Water Crystal's first ability)
I honestly won't be surprised if we see Vivi make it onto Commander's Game Changers list at some point, due to how powerful it can be