Padeem, Consul of Innovation
Legendary Creature — Vedalken Artificer
Artifacts you control have hexproof.
At the beginning of your upkeep, if you control the artifact with the highest mana value or tied for the highest mana value, draw a card.
Illustrated by
Foundations Jumpstart#62RareEnglishLegality
Rulings
The artifact you control has to have the highest converted mana cost only among artifacts on the battlefield, not among all permanents on the battlefield.
If an artifact has 
in its mana cost, X is considered to be 0.
If you don’t control an artifact with the highest converted mana cost as your upkeep begins, Padeem’s second ability won’t trigger. You can’t cast an instant to destroy an opponent’s artifact during your turn before your upkeep begins.
If you no longer control an artifact with the highest converted mana cost as Padeem’s triggered ability resolves, you don’t draw a card.