"Most of what they stole were graded cards, a load of single cards and a load of sealed, foiled packs
Muldrotha is in Sultai (black/green/blue) colors, giving you access to easy ramp, counterspells, and removal
It's clear this deck is running a historic theme , and cards like Alistair, the Brigadier, Peri Brown, and The Fourth, Sixth, and Eighth Doctors just drive that theme home
As cited by user CinnaToastKrunch on Reddit, they own +30 of them, showcasing just how much they admire the card featuring the Fighting-type Pokmon
If you want to buff this Commander Deck, other cards that make artifacts hexproof and/or indestructible could certainly be very fun, as barring a board wipe, this would prevent most damage, and help to keep your Commander alive, and annoying
Modern Ultra Rares Pokemon has added many rarity tiers over the years