The main gimmick is challenging other characters to battle but putting the currency that is used to unlock more capsule monsters (essentially gacha or gumball machine toys) up as the ante
If you like the -1/-1 effects, then Massacre Girl is another great option, with the added bonus of leaving you with a 4/4 menace threat afterwards
You can use one of your opponents Monsters as material
If you want to find a Pokmon product that balances rarity, design, and long-term value, Gem Pack Vol.4 stands out
You can build a finely tuned combo deck that wins on turn four with cold precision, or a Dragon kindred deck that spends six turns doing absolutely nothing and then suddenly blows out the entire table with an army of sky-lizards
Theyre not essential, but can add value if they fit your strategy