Overview
M99 is an RF whose sole purpose is to nuke the furthest target with her absurdly high burst on her Skill. Unfortunately, like other charged shot RFs, she has a long Initial Cooldown that hampers her ability to deal any significant damage before the battle is over. M99, like most others in this niche, can’t rely on how much damage she deals without her Skill either, since her ROF is severely crippled compared to general use RFs. This means that her most effective use is where she is against very specific bosses that have a low but not too low health pool, which are as of now very few.
Overall, M99 shouldn’t be used over more general purpose RFs, or RFs with shorter Initial Cooldowns on their charge shots. The situations where she is useful are so far and few between that she’s simply not worth the investment.
Pros
High Burst
M99 has an absurdly high Damage stat. When combined with her Skill’s high multiplier which is further boosted by her number of dummies, she will obliterate practically anything in her path.
Cons
Low DPS
M99’s high burst potential comes at a cost, which is her very poor ROF stat. Since her Skill isn’t a traditional Damage or ROF boost, she will go for long periods of time without dealing any significant damage.
Long Initial Cooldown
M99 has one of the longest Initial Cooldowns. It extends past the duration of most battles, -- especially when running RFHG Echelons --. meaning her skill comes into play very, very rarely.
Full analysis
M99 has a very high Damage stat of 157 but a pitiful ROF of 32. While certainly not the lowest in her class, or even her rarity, it does significantly affect her damage capabilities -- a fact that becomes all the more egregious when considering her Skill.
M99’s Skill, Steady Shot, has her take aim for 2 seconds, then shoot the furthest target from her for 8x her normal Damage. This Skill has an insane potential for burst damage, but it also has an absurdly long Initial Cooldown of 15 seconds and a standard Cooldown of 16 seconds means that it will hardly ever see use. There are only a few boss battles in the game that will last long enough for M99 to activate her Skill once, let alone twice, meaning that in most situations she might as well not have a Skill at all. When combined with her low ROF, this makes her one of the slowest mob clearers out of all RFs -- a distinction one definitely should not wish to possess.
M99’s tile buff, like other RFs, isn’t particularly notable, reducing the cooldown of one HG by 18%. This is fairly standard among 5 star RFs; though they may have some variation on the tile position, the buff is always the same.
In conclusion, M99 is not a particularly good RF. Inside her niche, she’ll demolish a high HP enemy in one quick burst after a long period of time waiting for her Skill to come off cooldown, but her uses are limited outside of these specific situations. Outside her niche, she slows down the mob clear of any RF team, making her terrible for general use. If one truly desires good boss burst, IWS or a charged shot RF with a shorter cooldown, such as Mosin and Springfield should be used instead.