Flash doesnt go the graveyard after it resolves
Valakut, the Molten Pinnacle's triggered ability has an "intervening 'if' clause." That means (1) the ability won't trigger at all unless, at the time a Mountain enters under your control, you control five or more Mountains other than that new one, and (2) the ability will do nothing if you control fewer than five Mountains other than that new one by the time it resolves
There is another promo version of Mickey Mouse, Brave Little Tailor, that is serialized and printed in gold foil art which is only given out to winners of the world championships
For example, I noticed that it can be useful in decks that focus on creature-based strategies, as it can copy powerful creatures and provide card advantage, as well as be a valuable addition to decks that utilize control or combo strategies since it offers flexibility and card selection
Not only is it a fun meta joke to have a card called "Card Collection" in a TCG, but this card also references the reward you can get in Final Fantasy XIV by collecting enough cards