Heat comal, griddle, or heavy skillet over low heat for árbol chiles and medium-low heat for cascabel and chipotle chiles.
For the arbol chiles, toast them, turning them over and pressing them down frequently with tongs, until they’re browned all over with some blackened spots, about 8 minutes.
For the cascael chiles, break each into about 3 pieces for easier toasting, then shake out and reserve the seeds. Toast the pieces, turning them over and pressing them down frequently with tongs, until they turn a lighter, slightly mottled red, about 1 minute. Remove the pieces. Toast the seeds in the skillet, shaking and tossing, until they’re lightly browned and fragrant, 20-30 seconds.
For the chipotle mora chiles, toast them, turning them over frequently, until dark, blackish blisters appear in spots (some will even puff up), 3-5 minutes.
Grind or blend the chiles (and the toasted seeds, if you’re using cascabel chiles) to a powder in a spice grinder or blender jar.
Store in an airtight container in a cool, dark place (not in the refrigerator) for up to 3 months.