I have been making a druid deck recently and need clarification on the mechanics of mutation. According to the wiki, improved mutation adds 0-4 atk and health to creatures like a mini chaos power. Most of the time, this seems to be true. Whenever I mutate a ball lightning, mutants generally have 6+ atk. However, when I mutated a rol once, I somehow managed to get a 7 atk dragon, which is more than 4+ the atk of a rol. Is the 0-4 rule true, or is it a 'most of the time' rule with a small chance of getting a 4+ increase in stats?