Raphael, the Nightwatcher can help finish a game on the spot with enough attackers
The rebacked and old proxy cards can easily be identified by their weight and thickness while the blue core proxies are of very high quality and are a bit hard to identify and need to be tested by looking at the details of their printing pattern and direct exposure to light for penetrability
Common Situations for Proxies Expensive Staples: If you need a playset thats going for 300 dollars, proxies let you practice before you decide to spend that much
The Masked Royal was limited to 100 copies in Japanese and 30 in Korean, and is my rarest and most expensive bought FA Supporter card, for which I paid 3.4k USD two years back (but is definitely also worth more than 5k USD now)
They have a good balance between cost and reward
A full party is when you have at least one creature of each of the four creature types (cleric, rogue, warrior, and wizard) on your board