Cards like [card]Kappa Cannoneer[/card], [card]Wurmcoil Engine[/card], and copied threats from [card]Phyrexian Metamorph[/card] apply steady pressure, while extra-turn spells allow you to close the game without giving opponents a chance to recover
Potentially you're handing out a second card to your opponents (or all of them) which is dangerous
For example, you won't be able to cast another creature or activate Hexplate Wallbreaker's equip ability between combats
High rarity pull structure
Cards like Lilo, Making a Wish and Stitch, New Dog were just two of the many cheap threats packed into the amber/x aggro shell, with the purpose of getting characters into play as fast as possible, and then using some number of Lanterns or shifting using Stitch, New Dog to get Stitch, Rock Star into play ahead of curve
For those who enter Pokmon TCG tournaments, the only way to legally use Japanese Pokmon TCG cards in tournaments is by crafting an entire deck of Japanese cards