Chancellor of the Forge is a game ender.  If you have Purphoros in play with two creatures that can make token copies of a creature, then cast Chancellor of the Forge, it will give you four 1/1 Goblins, netting you five total ETBs for Purphoros.  Use one of those two creatures to make a token copy of C.Forge, then it makes nine more 1/1 Goblins, putting us at 15 total Purphoros triggers for 30 damage to each opponent.  Copy C.Forge again and we're at 68 total damage to each opponent.  Probably game over.  And with a deck like this, you might only need to copy it once with all the other creature tokens likely to be in play.  Heck, you might not even need to copy it.

Golden Argosy is a very underrated card, and it shines bright in the right builds... for one, it flickers a lot of creatures at the same time, returning them at the end of the turn, which is great for abusing ETB triggers... like Purphoros's trigger...?  Huh.  But the hidden value is that you're removing your creatures until the end of the turn, which is an ideal time to board/creature wipe!  The Argosy is a worthy sacrifice to save all your other nontoken creatures, especially in a deck like this where a lot of them will be triggering to create more tokens anyway.

Gleefull Demolition and Kuldotha Rebirth (and Devastating Summons) can be finisher cards, where three more triggers from Purphoros is enough to end the game or knock players out, for an unsuspecting one red mana.  Maybe you snuck in Dictate of the Twin Gods before your turn began, with Purphoros already in play, then proceed to cast Fiery Emancipation on your turn, but only have one mana left available after... Gleefull Demolition and Kuldotha Rebirth dole out 36 damage to each opponent for one mana.  That's game over territory.  And if you can't cast that "finisher" spell, in all likelihood, something on your board will get removed, if not all of it, before your next turn, so being able to use one mana to that great of an effect is worth keeping in your hand for the ideal moment.  Firecat Blitz's flashback is the same thing for two mana, and you get as many creatures as you have Mountains available to sacrifice, which sounds scary, but not if that means it's game over.  But yeah, it hurts if it gets countered...... but then, there are game moments when you know no one has any counterspells left, or they would have been used, or maybe you have Tibalt's Trickery and Firecat Blitz is sitting there waiting in your grave to be abused.  Is it worth including...?

The fun thing about Mirror-Style Master is that it triggers on attack, while there are a range of other ways to make token copies of creatures with haste before declaring attackers.  That means you can potentially make extra copies of Mirror-Style Master before attacking, having each put a +1/+1 counter on an unmodified creature when it ETBs, then each Mirror-Style Master and each Backup-modified creature makes a copy of each modified creature!  Talk about some shenanigans!!  If you can make token copies before declaring attackers, make copies of this!!  You're welcome.  Once people realize the power of this card it will go up in value.  Just saying.