MUR cards have a different texture: smoother, metallic, with light-catching properties that shift as you tilt the card
(It can't be blocked except by two or more creatures.) If the target creature isn't both attacking and equipped when Item Shopkeep's ability tries to resolve, it won't resolve and none of its effects will happen
It can do this simply through its Bloodthirst X ability, which goes insanely hard in Commander
Company: Wizards of the Coast Release Date: November 17, 2017 Brand: Magic The Gathering Item Type: Single Card Series: Iconic Masters UPC: Stock #: 177579 Our Guarantees to You, Our Valued Customer
The classic old-school combo with Marton is Maze of Ith, and you can also slot in the modern-day version Labyrinth of Skophos
Your opponents creatures entering the battlefield tapped is great protection against creatures with haste, especially scary ones like Thraximundar