Stella Lee is efficiently costed so she can come out early, with a strong defense for blocking and built-in card advantage, while Eris gives you one of the deck's few ways to actually hurt your opponents
It is an old medieval German city with tons of great inspiration for all my fantasy illustrations
You also cast a sorcery to trigger things like Guttersnipe and you make an artifact for things like Goblin Welder, so it fits into both the Izzet Spellslinger theme as well as any deck that includes Red that loves artifacts
Most Grapeshot decks have a ton of cantrips, spells that have an effect and then draw you a card for a low mana cost, letting you dig deeper into your deck to find your copies of Grapeshot
You can have him sing Bibbidi Bobbidi Boo, return him to hand, play him again for free, bounce him with another card, play him again - all in the same turn