Larvesta from the Darkness Ablaze expansion is a decent representation of this, as its Singe attack guarantees a Burn on the foe and only requires one Fire-type energy to play, making it an optimal card to use at the beginning of a battle
It's like the realized it was terrible and cut all the cards that had the ability, but they were proud of having created a "new" ability so they couldn't axe it completely
Battles can be cast during your main phase if the stack is empty, just like creatures, sorceries, and other non-instant spells
While these machines often focus on plushies, apparel, and other Pokmon Center merchandise, some also offer TCG products
Shardless Sultai seems to come in and out of favor in Legacy, so there is demand there for the Agent but I think that is mainly coming from casual players