Granted, those decks are almost all focused on milling out the opponent but the original Hedron Crab is also able to target yourself, which makes it one of the most explosive and mana-efficient self-mill engines ever printed
The order of the colors doesn't matter, so the effect will activate for either yellow and black or black and yellow
Each colour is associated with a strategy: Steel hits hard, Sapphire is slow and strategic, Ruby hits fast but weak, Emerald is about thinking beyond the playing field, Amythest nerfs your opponent and Amber heals and buffs your deck
If you're looking to find any of these cards, rather than buying them outright as singles, then you'll want to pick up some Winterspell boosters ASAP
If this Deck manages to go first, it will be extremely hard to defeat the Spright monsters that have swarmed the field because of their negates
If the equipped monster would be destroyed as a result of battle, destroy this card instead, and make the Battle Damage to the controller of the equipped monster 0