They often let other merfolk be played from the library, create merfolk tokens when their allies enter the battlefield, or have ways to protect each other that quickly add up
Since 1996s Mirage, Charms have been an indelible part of Magic, even inspiring multiple new cycles like Cryptic Command and Mystic Confluence
As part of the Making Magic (2003-2005) article series on the game's official site, Mark Rosewater described each color in depth (as well as multicolor cards, artifact or colorless cards, and color-hybrid cards)
Hes got a new Power-Up mechanic, which is basically an exhaust ability that gets cheaper if you use it the turn he enters
PS: maybe an idea for finding the missing cards: compare the LQ images downloaded by Forge with your images (comparing the same directories like "4E", "5E", ...)