(There was a time when there was no maximum limit, which swiftly changed after someone entered a German tournament with a 2000+ card deck.) A tournament deck will always be 40 cards because the fewer cards you have, the more likely you are to draw the ones you want
8 Tempest, Dragon Ruler of Storms is Useful in Specific Strategies First Printing: Lord of the Tachyon Galaxy At one point in the early 2010s, the Dragon Ruler strategy was by far the best deck in the game, and this led to many of the cards in the archetype seeing considerable time on the game's Forbidden & Limited Card List
Banlist History Restriction changes recorded for Mimicking Man-Eater Bug
Bio-Armor: Full Armored Crystalzero Lancer wears armor and wields weapons derived from parts of Black Ray Lancer
This means you get the full effect if you get it early
I then waited until the right moment, and played Return of the Nightstalkers