Swords, Path and Crib Swap are all as welcome in Slug as they are in Hug (and most other EDH decks)
It also pairs nicely with Emerald's other discard synergies, giving you more ways to shred your opponents hand
Ancestral Mask can expedite how fast its power grows with an additional +2/+2 for each enchantment on the battlefield
While I personally wouldnt say this is one of the top five blue cards in Modern, it has been a solid addition to Grixis Shadow as it can combo with Deaths Shadow to create a 13/13 creature for a turn irrespective of your life total, as well as being a solid addition to sideboards of many blue decks in the format
Royal: Enchanted creature gets +1/+1 and has ward 1
Casting of Bones was similarly problematic, as its always risky to put something like this on your creature, when it could be removed in response and Swords to Plowshares was the removal of choice anyhow