I wanted the deck to not be completely terrible, so it has some power cards to make up for the army of subpar pegasus commons
The card has seen some renewed interest following the banning of Land Tax as potential card engine replacement (also mentioned in the Premodern blog recently)
Different ones fit different decks, but Trinket Mage stands out for its ability to get cheap, powerful artifacts
For Hearthhull, I think it comes down to the fact that this deck is dumping tons of lands into the graveyard and it most likely wins the game by bringing them all back in one go - using a card like Splendid Reclamation - for a mass of triggers
If damage would be dealt to Bloatfly Swarm while it has a +1/+1 counter on it, prevent that damage, remove that many +1/+1 counters from it, then give each player a rad counter for each +1/+1 counter removed this way
It's power befitting of the Ultimatum name