Mirror-Sigil Sergeant

Normally, when a token is created by this ability, it will simply be a Mirror-Sigil Sergeant, so it’ll also have the token-creating ability. (See the other ruling for weird exceptions.) At the beginning of your next upkeep, if you still control the original Sergeant, the token copy, and a blue permanent, you’ll get two more token copies; the turn after that you’ll get four; then eight; and so on.

The “intervening ‘if’ clause” means that (1) the ability won’t trigger at all unless you control a permanent of the specified color, and (2) the ability will do nothing unless you control a permanent of the specified color at the time it resolves.

Here’s the detailed version of what happens. As the token is created, it checks the printed values of the Mirror-Sigil Sergeant it’s copying — or, if the Mirror-Sigil Sergeant whose ability triggered was itself a token, the original characteristics of that token as stated by the effect that put it onto the battlefield — as well as any copy effects that have been applied to it. It won’t copy counters on the Mirror-Sigil Sergeant, nor will it copy other effects that have changed Mirror-Sigil Sergeant’s power, toughness, types, color, or so on.