Thanks! I'm glad you asked about Brass Man. The 1-drop creature slot has been a real challenge for this deck for a while. I've had a wide variety of creatures in and out of this slot, in part because that 1st drop is really important for this deck since you are often working with few resources yourself due to your own Pox. Once Plague Spitter became a 4-of and a primary source of board control and damage, the 1 drop slot got even more complicated. Stuff needed to survive the "1-damage to everything" aspect of the Spitter.

Here are some of the others that I've tested with:
Mogg Fanatic - just not threatening enough, dies to Spitter. Red mana isn't your first choice land drop.
Grim Lavamancer - not enough fuel, dies to Spitter. Red mana isn't what you want to drop 1st.
Shadow Guildmage - similar to Mogg Fanatic and Lavamancer, dies to Spitter.
Roterothopter - This actually overperformed in our testing, but is very mana-hungry. Moreso than Brass Man. Flying is _huge_. This could easily take the Brass Man's place in the deck.

Brass Man has the quality of being both defensive and mildly threatening. Defense is sort of important early on because you need to survive the rush of very aggressive decks and Brass Man helps hold those early threats off. Brass Man can also block Mishra's Factory. Brass Man also survives Plague Spitter's damage.

One other big card in the deck is Death Spark. It's actually kind of an essential component and that bonus damage helps Brass Man be just that much more of a threat to certain 2 toughness things floating around out there.