Here are the weird exceptions. If any copy effects have affected the Mirror-Sigil Sergeant whose ability triggered, they're taken into account when the token is created. For example: -- If Mirror-Sigil Sergeant's ability triggers, then Mirror-Sigil Sergeant temporarily becomes a copy of another creature before its ability resolves (due to Mirrorweave, perhaps), the token will be a copy of whatever creature the Mirror-Sigil Sergeant is currently a copy of. After the turn ends, the Mirrorweaved Mirror-Sigil Sergeant reverts back to what it was, but the token will stay as it is. -- If the copy ability of a creature (such as Cemetery Puca, perhaps) makes it become a copy of Mirror-Sigil Sergeant and gain another ability, the token created by this creature at the beginning of your upkeep will be a Mirror-Sigil Sergeant with that additional ability.