As we alluded to before, these four cards are from The Lost Caverns of Ixalans accompanying Commander set
Professor Hojo's first ability reduces only the amount of generic mana in the first activated ability you activate during your turn that targets a creature
You have 2 mana to start the Hydra and then XX in the cost
Disney Put simply, the game is a race to get 20 points by using the actions, songs, and characters that are on each card
It just uses the word, "Swamp." Another good example is extort, which has the Black and White symbols in the reminder text, or a fetchland like Mountain Valley that clearly is Red and Green in flavor and mechanically, but is allowed in decks without Red or Green
They didn't use spears or any kind of polearm, instead relying on more on a firearm called a Dragon