In elder's recess where teostras's home is, Teostra and Lunastra were forced out of its den by Crimson Fatalis and inside of the den, the inferno was surrounding him which was so hot that it melted the surrounding rocks to lava, showing the full moon and his veins were glowing orange due to Immense Fire energy within him and was slowly charging its energy. This is a massive threat and even by Fatalis standards the most dangerous version especially when he is in his Crimson demon state