The old master was terrified, summoning a familiar wasn't difficult but summoning a familiar with the flames of hell represented the power of the celestial master. The one who could summon white flames familiar were the most standard celestial masters, those who summoned red were in the second stage as they can burn a person to a crisp and the one who summoned black could even turn a person into ashes with just a small move of their hands but the one who could summon blue flames were the one who was the most terrifying.
They could not only control the powers of hell's flames but they can also use the powers of the other flames, they can burn, explode and melt anyone as they wish.
As far as he knew, only a few celestial masters could summon the deepest and hottest flames of hell, and those who can summon the flames and even morph them into familiars were even rarer, for a celestial master to do something like this, it can be seen that they are rather powerful.
