Business Snail was added in Beta 50.0. Previous Versions can be found here.
Released alongside Snail Pen, both these Snails have stats bigger than the 1/1/1 the original 3 Snails (and the also newly released Burning Snail) have. Both also have a passive effect instead of a Magic.
In Business Snail's case, it's a 2/2/2 that passively gives +1 cost to all Snails in your hand, but also +1/+1 to all other Snails on your board, making them all at least either 2G or 2/2 themselves (as when they appear on the board, their cost returns to normal).
Since Business Snail is 2G by default, it will only gain Haste from Blue Snail and is unable to be summoned by Thundersnail or Snail Bucket. Also, it's able to be targeted by Burning Snail due to being a Snail, despite not having a Magic effect, thus failing it (even if you have one or more Snails with Magic on the board).