To trigger the Meld mechanic, a player must own and control both cards on the battlefield, and then pay seven mana of any color
Erode is another one mana white removal spell that provides a hard answer to a creature
PSA checks for chipping, whitening, fraying, and any rough spots
In the end, it was killed because we decided that we didn't want to force players to track down specific versions of cards for tournament play
The first time person who ever activated Karn against me was Level 3 Judge Ben McDole, playing it in his Progenitus Superfriends deck
If you were to have a land type count as that color instead, you would allow Mtenda Lions and such, but disallow many more things