For example, if the card is a land, I say Lands need to have a downside, like entering the battlefield tapped, because otherwise it produces really overpowered lands
That card is obviously super-strong, but imagine if it was not a Supporter, and thats exactly what Gust of Wind is making it an exceedingly powerful Trainer card from the TCGs first set
A deck focused on Spellbook cards would greatly benefit from including Hierophant of Prophecy, as it has the potential to clear multiple Spell/Trap cards from your opponent's field in a single turn
Soulbond Soulbond is a mechanic that establishes a link between two different creatures
If its casual, are gold-bordered cards okay
You also get a fake polaroid picture showing Cynthia and her Garchomp, as well as a bunch of standees featuring Cynthia, Garchomp, and other Destined Rivals Pokmon