Next to the individual Pokmon stats (such as HP, Strength, Defense, etc), these types determine what each creature's strengths, abilities and weaknesses are
Market prices for individual cards fluctuate wildly depending on supply and demand, so using platforms like TCGplayer is a smart first step before listing them
When City of Ass was printed, mana burn was still a thing (unspent mana would deal damage to you), so the extra half mana would harm you and in a way work like City of Brasss ping when tapped
They each gain one lore passively, and each have an impressive four willpower, meaning theyre hard to take out in a challenge
High scores are tremendously important to people who are looking to appeal to serious collectors, as it can be difficult to find certain rare cards that are still in good condition