it's simple, and its about what youd expect from the name
C Common Metal Detector X TRAP You can activate this card when a Continuous Trap Card is activated
Kor Shyfisher also starts to look good in your deck when you have the things to make the Hawk good
If you take a Pokemon on the Bench, you still get the point for the KO, allowing you to use Articuno to finish off weakened opponents, even if they retreat: while 10 damage isnt a lot, it will quickly rack up round-on-round, especially if they are already damaged
Historically, this came about because Wizards R&D would use B for black and L for land, so U became the shorthand for blue and it's been that way ever since
Legacy players have a huge pool of powerful removal spells, so having the option to have protection from half of them isnt going to get you anywhere these days