Once you choose a creature to sacrifice, it's too late for players to respond
When cast, Tiamat can find up to five Dragon cards that each has a different name and put into your hand
The odds of a player making Top 64 in a Swiss tournament like this is based on their win ratio versus the number of rounds - so when that number is abruptly truncated with no prior warning, their chances change
What you need is standard retail paperwork: a registered business, a tax ID, and a state resale certificate (seller's permit) so you can buy wholesale without paying sales tax up front
after all, it's to be cast right away for zero mana, and then again much later, after players have exhausted their hands of board-impacting plays and are searching out more gas
All in all, it's a very straightforward, but very potent recipe for victory