Oops. I forgot to mention about it but it was in my mind when writing the stuff up. :P
You don't necessarily need a Pokemon that can use Rapid spin, but if you don't, you need to be prepared when having a Pokemon that would be 4x weak to it, such as Talonflame or Charizard. The trinity are entry hazards, magic bounce, and rapid spin. You may at least want two out of the three but it's not always needed, but such things like Stealth rock are good versus pokemon with Sturdy or Focus Sash.
RNG stands for Random Number Generator. You could consider it to be the luck factor to all games, mainly RPGs. Despite being called a RNG, the values are fixed during certain events. Take Pokemon for example, (I used an emulator to test this) when in battle and you choose a move with that does not have an accuracy value of 100 or higher, the move will either hit or miss. Using multiple save slots, I was able to determine that any move outside of the 100 accuracy range, if a move hits, any other move would have also hit during the time. E.g. Ice Fang w/95 accuracy and Sheer Cold w/30. If Ice Fang hits, Sheer Cold would have also hit had you chose that instead. If Ice Fang missed, Sheer Cold would have also missed as well. There are other factors that could have caused your other attacks with 100 accuracy to miss as well, such as Double Team, sand attack or Bright Powder, in which if the move with 100 accuracy misses, the others will miss. You could say it isn't really all that random but it's annoying when it determines whether if you win or lose most of the time, especially in online battles.
People like to call the RNG a goddess for fun and label her as a supreme entity. She can give you all the luck you want or bring you pure misfortune. No matter how good you are at a game, she can instantly screw you over.
