The Maybeboard has cards that fit the deck but can either be blitzed in for a limited effect plus a draw, or cast normally for longer-term benefits as well.  They are not second-tier cards, but they are not just a blitz target.  Many of them are excellent in this deck.

Ebondeath, Dracolith is essentially only good for drawing a card on each player's turn, via blitz, if you can afford to 2 black mana each time, and if a creature died that turn (sac one if needed?).  But that's pretty handy if you find yourself with your board wiped and a small hand, but lots of mana, as this guy just sits waiting in your grave... you just need Henzie in play to get it going, and creatures dying.  And if you have a sac outlet in play, you can cast Ebondeath multiple times in one turn, maximizing your opportunity on an opponent's turn once a creature dies.  Sadly, as a blitz target it only has card draw and sac-outlet-target value, as it will almost never come in with the ability to attack or block.  Pair it with Ashnod's Altar and Chromatic Orrery (and Henzie, of course) for unlimited card draw.

Mitotic Slime is a great blitz target if you have a sac outlet to abuse, as it will provide the blitz card draw and seven sac targets, if you don't want to use the creature tokens for attacking/blocking first.  That's a decent amount of value for 2-4cc.

Gorex, the Tombshell is another prime blitz target... exile two creatures reducing his cost by 4cc, blitz him in the reduce it by 1-2cc, and cast it for 2-3cc... attack and get one exiled creature back, then sac him to a sac outlet to get the other exiled creature back and draw a card.  This should never cost more than 1BBcc, and usually only cost BB to cast... to recur two creatures, draw a card, and attack with a 4/4 deathtouch (i.e. kill a creature or deal 4 damage)... that's crazy good value!!

Any creature that has a "Champion a creature" ETB trigger can be used to flicker another creature to get an ETB trigger from that one too.  Without blue and white it's not easy to flicker creatures, so getting creative like this can have its value.

Keldon Firebombers seems like a bad idea, except that it's realistic to deck a few cards that can put all your lands in your graveyard into play, since we'll be drawing lots of extra lands that we can hopefully discard for fresh card draws.  If you draw one, then having this guy (search for it) can almost be a wincon just by how much it'll slow everyone else down.