All of these are just different ways to say you can cast this for something other than whats printed in the top-right corner. Examples of Alternate Costs Let's look at a few major mechanics that are alternative costs
The one on the left comes in English with black borders, Spanish and French with black borders, and Spanish again with white borders
Physical Cards Only The Reserved List only applies to physical, printed cards
You can expert merfolk galore, but also some more unusual fantasy races like puffer fish people, penguin people, crab men, walrus women, and something that I would swear was an underwater sliver, if it didn't have the wrong number of limbs
All decks find themselves needing to take some care with their life as there are so many powerful things that can end games out of nowhere if you don't