The most interesting thing here is the ability text, and although its unusual to see this in blue, its just not something thats usually going to be useful
What makes this specific card so rare is the case being signed by artist Mistuhiro Arita
The controller wants to defeat the Siege, because once the Siege's last defense counter is removed, it is exiled, and its controller gets to play its reverse face for free
Its been more common for WotC to create new subtypes than main types
Blood Moons out to make it a nightmare for your opponents running multiple nonbasic lands by turning them all into mountains
Perhaps they sacrifice something with stun counters or their +1/+1 counter-pumped creature gets removed, each of these situations results in treasure for you, so it absolutely feels like you're stealing