In "Magic: The Gathering", what instant card has the highest converted mana cost?

In Magic: The Gathering, Blinkmoth Infusion has the highest converted mana cost among instant cards. This card has a converted mana cost of 20, making it considerably expensive to cast. It allows the player to potentially gain a large amount of life, equal to twice the number of artifacts they control. Additionally, it has affinity for artifacts, meaning its cost can be reduced by the number of artifacts the player controls. However, despite the high converted mana cost, Blinkmoth Infusion offers a powerful effect in terms of restoring life and can be useful in artifact-based strategies.