"Destiny End Dragoon" was initially stolen by Mike in the fourth season, but it was retrieved by Jaden and Emeralda during a Duel that Mike organized, and was ultimately returned to Aster
Legality depends on the tournament format -- Sivitri, Dragon Master can be legal in some formats and banned or restricted in others
The Strategy Alania, Divergent Storm wins by casting a ton of spells and copying them a ton of times
Shadowless Sealed First Edition Booster Box, $432,000 With the Shadowless Charizard as the key card, buying raw boxes and going hunting became fashionable
Field of Ruin is already seeing a ton of play in Modern, but thats because Modern is a format where your lands are incredibly important (and there arent a ton of basic lands to search out)
Copying big spells is all kinds of hilarity, whether its a nonlegendary creature or Jaheiras Respite (now requiring half the number of attackers)