Japanese sets usually arrive months before international versions, placing early copies into the market when interest peaks
Well, I like to just pick the card back up (likely from the graveyard) and just keep on re-triggering the ability till my opponents buy what Garys selling
You want to play the right type of Pokmon against your opponents types to get a type advantage and do double or triple the amount of damage your Pokmon would normally do. Trainer cards (including Supporter, Stadium, and Item) are cards you can draw from your deck to gain an advantage
Other applications would be in decks with creatures that have powerful enter the battlefield effects such as Elite Spellbinder : being able to recur those effects can become such a headache for opponents who basically have to deal with them twice
It has 270 HP and can be played immediately since its a Basic Pokemon
Obviously thats hyperbolic, as animating a land isnt quite as valuable as getting an entire token out of nowhere, but getting a land creature is closer to the Mentors trigger than you think