As a very general rule for Limited, I would look to play something like this: 1 mana: 02 2 mana: 46 3 mana: 35 4 mana: 24 5 mana 13 6+ mana: 02 That's far from hard and fast, but it's a good place to start
Mayhem is pretty similar to madness, only that it forces to player to follow timing restrictions
Secret Rare Cards: Name: White Explosion Effect: Synchro Summon, 1 Synchro monster using non-tuner monsters you control and 1 tuner monster in your hand as Synchro Materials
To do so, you must show your opponent your entire hand, proving that you didnt draw a Basic Pokemon, and then shuffle all 7 cards back into your deck
Donts: Making Decks around already existing series, from other card games or animes/games etc
A fluctuating tournament metagame, generous modern print runs and the threat of sudden reprintings mean that collecting cards from this millennium is closer to day-trading than building a stable portfolio