The idea behind this rarity system is that the rarer the card is, the more sides its symbol will have
That alone is horrific enough for Toxrill to earn his creature type, but the fact that he can consume the slugs he births in exchange for cards takes things to another level of disgusting
Since its a lesson, its easy to grab from the sideboard, so its a great toolbox option
Several of these cards can still see use like Shambling Cie'th, and Dreams of Laguna
I gushed about Ancient Cellarspawn in the rankings, and Im likely too high on the card, but its definitely a shoo-in for horror decks
Last but not least, in Raise of the Floodborn there are many more cards that exploits the Shift mechanic introduced in the First Chapter