Military action
The Diabolous finds and kills a student in the Templar School of Ascension. He continues the school in his place to rise up the ranks and become the Supreme Templar. He uses his power to militarise the Templars as per the Lord's will.
The School of Ascension is where students are trained and taught about how to be the Supreme Templar as one of them would graduate to become just so. One student was Michaelon, a well respected student who befell tragedy. One dark night, he met a strange figure in Deorum and asked what the figure was doing. Unbeknownst to him, this figure was the Diabolous. A fight broke out between them which the Diabolous won, killing Michaelon. The Diabolous proceeded to attend the School of Ascension in his place and was doing exceedingly well with his vast knowledge and battle prowess. He worked his way up and saw the recent skirmishes as an opportunity to climb higher in the ranks. He orchestrated more intense attacks at certain points across Adremesis to put many Templar generals in grave danger so he and his peers could take those positions of power in the meantime. This worked very well for him and he graduated as the best and so took the position of Supreme Templar. He promoted many of peers around him after the skirmishes and indoctrinated them into his malevolent ideals. The Diabolous militarised the Templarhood by offering many initiatives for people to join them. He selected a personal army of the Supreme Templar who would be the ones to move forward into the Lord’s plan with the rest as cannon fodder. People grew suspicious of the change in the Templarhood, but nobody could have predicted that the Supreme Templar was a Diabolous.