"Iwata Asks : Pokmon Black Version and Pokmon White Version 2 : The Three Sacred Treasures"
Whenever a creature you control attacks or blocks, it gets +X/+X until end of turn, where X is the difference between its power and toughness
The honest answer is: if you have to think hard about the price difference, play boosters are probably the better fit
For example, if you discover 4 and reveal Galvanic Giant (an adventurer card from Wilds of Eldraine with a mana value of 4), you could cast Galvanic Giant, but not Storm Reading (its Adventure, which has a mana value of 7)
It's also perfectly fine to play it face-up as an evasive attacker
Brawl Legal Vintage Legal Timeless Legal Commander Legal/GC Pauper Not Legal Oathbreaker Legal Penny Not Legal On the Commander Game Changer list (view all) Toolbox Buy This Card Notes and Rules Information for Adis: Only the English version of a Magic card receives Oracle updates and errata