An altered Magic card is still legal if the original text denoting the name of the card is unobscured, and the paint isnt too thick to alter the thickness in shufflingthough this is ultimately to a judges discretion, and they can refuse altered cards entirely
If you're playing an aggressive or midrange tribal deck and you're only including sixteen creatures, you have to ask yourself: "Is it even worth playing all of these tribal cards in the first place?" If, for example, you only have enough creatures to have a couple in play at any given time, you're not maximizing your tribe's abilities
Identifiable by the black dot at the bottom of the card in the copyright text (specifically on Nintendo), this is easy to identify when you know where to look
Red, and to a lesser extent, black had flips that we could cost more aggressively
Origin Forme Dialga VSTAR #GG68 from Sword and Shield set Crown Zenith