An archetype could also be based on a specific word that's found in the names of all the cards in it, like Swordsoul, Therion, or Marincess. There are hundreds of different archetypes since they first started making them in the late 2000s
Beyond that obvious pair lurks the often forgotten Panoramas from Shards of Alara
Assuming all "standard size" sleeves are identical: They're not
The 5-cost Nami can force the opponent to add a Life card to their hand, making them more vulnerable to your attackers 9-cost Boa gives us more survivability while putting your opponent behind on Life cards
There are five Welcome Decks, each containing 30 cards of one color, focusing on simple gameplay
If several creatures enter the battlefield under your control at the same time, Leyline of Vitalitys triggered ability triggers for each of those creatures