Overview

SIG-556 is one of the rare few ARs who can cap their own RoF during Skill activation, and she gets a considerable Damage buff during it as well; this means SIG's skill is somewhat similar to the Charge Focus skills from TAR-21 or ART556, though with a heavier focus on RoF than Damage.

• Notably, SIG-556's skill just sets her RoF to max instead of being a % boost, and effectively has a fixed duration at all skill levels. This means SIG-556 can provide her full burst even without a high Skill Level, so she can work very well without heavy Training Data investment. A new player who's lucky enough to roll her will easily see SIG-556 outcompete other ARs in the early stages of the game. 

Most of SIG’s stats are slightly above average, with the exception of Accuracy, where she falls somewhat behind. With rising enemy Evasion values, this is becoming somewhat more relevant, although a bit of attention when teambuilding (or using a Fairy with Accuracy in its aura) will largely alleviate any major hit rate issues. SIG-556's Tile Buffs are likewise moderate but good, providing 15% Evasion which is always appreciated by SMGs; the slightly less useful Rate of Fire is at least better than nothing. 

Battlefield Wave is SIG’s unique skill and primary selling point, which operates on a toggle. The initial state provides her with the dual benefits of a Damage buff and maxing her Rate of Fire, but comes with the minor downside of accumulating stacks of ‘Overload’. Overload stacks once per attack, which when stacked to 12 will temporarily stun SIG and reset all stacks. If Battlefield Wave is toggled to the Inactive state before SIG-556 stuns herself, Overload stacks can be removed at a rate of 1 per attack.

• With some manual attention, Commanders can control SIG's burst more reliably than Auto Skill and gain a small but meaningful increase in DPS. 

SIG 556’s biggest downside is her high rarity, which is somewhat offset by needing lesser Skill investment than some others in her niche. Like all 5-star rarity ARs, SIG-556 needs a cost of 105 Cores to fully link, which can be quite expensive as SIG-556 is the most useful in the early stages of the game. This is nonetheless a good investment when players have few AR options, especially since those options they do have are stuck with substantially lower RoF. As a Commander’s AR arsenal grows and free options such as AR-15 and M4A1 (both pre- and post-Neural Upgrade) start to come into their own, SIG’s usefulness starts to fall off - though she remains a very competitive DPS AR among 5-star options. 

SIG-556 is far from a bad unit, albeit her odd skill may require a bit of personal attention in battle to reach her full potential. Nevertheless, in the crowded field of overwhelmingly powerful ARs in the endgame, she can struggle to make enough of a splash to stand out from the crowd or justify picking her over other ARs - she only performs slightly above average there. 

So do I auto-skill SIG-556 or not?

Auto-skill lets SIG-556 cool off some of her own shots by automatically turning her skill off when needed, but this in reality negatively impacts DPS because SIG stunning herself to remove 12 stacks actually costs you less DPS compared to having to attack 12 times with no buffs to remove it. See this CN comparison video between SIG-556 auto-skill and manual activation after stun and it will become clear that letting SIG-556 stun herself via manual skill activation yields better results. 

Fortunately for the lazy players, the difference is fairly small in practice. While it gets larger if SIG gets any RoF buffs, you wouldn't want to give her any in the first place, so this isn't much of a practical consideration. You can treat SIG-556's skill as effectively giving you a 50% Damage and 50% RoF buff, with uptime worse that of Damage Focus T ARs (10/16) but better than that of Charge Focus ARs (5/16).