If you have a shared creature type in your deck, or even just one singular threat you really must resolve, you need to be rostering four Cavern of Souls ASAP
If your opponent tries to destroy it again later that same turn, you won't be able to rely on the same card or ability a second time Regenerate Creates a Replacement Effect Regenerate is, at the end of the day, a replacement effect, which means it replaces one event with another
The restriction to the colorless identity is significant and made up for by rampant mana rocks that make high-cost spells easy to achieve
The only downside here is the cost requiring three colours of mana
The quantity sold depended on how many people offered to buy but was limited to a certain maximum
If you don't have a copy of the card in question, the next best thing is a card from the same set with similar attributes, like color, rarity, or foiling