The following is Team Ryujin's initial proposal for this unit. Any feedback and playtesting that you can provide us with will be greatly appreciated, and will be carefully considered by the team when deciding whether the unit's card is ready to finalise.
Long Lance Torpedoes - Each torpedo hit rolled by this unit deals 1 extra point of hull damage.
Antiair Barrage - This unit can make two Antiair attacks against separate targets during your Air Defense phase. This unit has a 5-dice Antiair attack against the second target.
Scout Cruiser 2 - At the beginning of your Air Attack step, you may choose two enemy ships in the same sector. Your units roll one extra attack die when making Bomb or Gunnery attacks against those Ships this turn. --------------------------------------------------------------
I like this. I'm actually kinda glad to see there isn't a Seaplane Detachment SA on this vessel after all. Nice to see the class limit of 1, and I'd say that given the strong SAs she has that a cost of 22 is about right.
Tone is well and truly obsolete, but it mostly already was, so I am not complaining.
This will be a nasty unit when you have extra fighters lying around without anything to do. You can now scout both the important ship in a sector (for your bombers) and the destroyer accompanying it (for the fighter not having to escort).
For what this unit can do I believe the unit is undercosted. Not even comparing it to they Tone (overcosted) or Gotland (undercosted), it just smells of power creep.
1) This unit becomes the third unit in the game to have Scout Cruiser, and the first to be able to use it on two ships in the same sector.
2) This unit maintains a 3/3/2/1 LL Torp line, which is usually at a premium and why Japanese units generally tend to cost more.
3) The gun/torp/armor line is comparable to the Aoba (20pts) with no flag, no Aggressive Tactics, the new Mogami has better AA, adds in Anti-Air Barrage and Scout Cruiser 2 for only 2 pts?
4) It's only 1pt more expensive than the Chikuma, and 2 pts less expensive than the Myoko (all of these can't be overpriced).
The original Mogami was 18pts, it loses some power from the mains and Determination. But it's gaining more versatility and defense against air with the ability to help damage your opponent from the safety of being across the map. At least with Scout Planes SA you can shoot and remove the counters, there is no counter to this (other than shooting down the attack planes)
With what the unit brings to the table, I think it should be more in the 24pt range, no lower than 23. It makes a Japanese Air build much more devastating and would be considered a 'must have'.
Costing of Japanese LL cruisers were messed up by Haguro. We've had to deal with that since then. But I like to see Nachi as kind of a reasonable base for costing.
Aoba is tricky (b/c of its SA), the original Mogami did not have Determination (just Tough Cruiser and Bad Luck), and Myoko is a horrible set 1 cost (recosts typically drop it at least four points to 20). Also, Scout Planes SA (for torps) does not have a counter that can be attacked in the RAW. That may be a house rule... but there is no mechanism within the game to do so.
Chikuma is a pretty well known entity so not a bad comparison. She is a requirement in any LL build, so she can sometimes seem to carry more weigh then her cost justifies, but that also often means keeping her out of the fray until late, limiting her impact.
Side by side comparison to Chikuma, Chikuma gets the edge.
Gunnery: They have similar mains/seconds when factoring in the SAs (granted these SAs may not always be used on the ships they are firing at, but that is mostly irrelevant to this discussion).
Mogami: Mains 8/8/7/5 (9/9/8/6 with SA); Seconds 4/4/3 (5/5/4 with SA) - both mains and seconds could be boosted with the SA.
Chikuma: Mains 9/9/8/6 (10/10/9/7 v Destroyers); Seconds 4/4/3 (5/5/4 v Destroyers).
I will give this to Chikuma as a win, because while Mogami can get boosts against any ship, the mains will never be better than Chikuma (and could still be worse) while the seconds on both are likely to target Destroyers, giving Chikuma a natural boost while Mogami has to use its SA.
AA: Mogami wins easily. As a typical backrow unit, AA Barrage is a nice help. But it has to be against a different target than the first AA, and it is only 5 dice. That's a 24% chance to abort a typical 5 armor bomber (44% against 4 armor). If I am doing the math right, between both attacks there is about a 63.5% chance of aborting one 5 armor unit and a 12.5% chance of aborting two.
For comparison, 8 AA dice will abort a 5 armor plane 64% of the time, so 7 AA + 5 AA is roughly on par with 8 dice. I will give the edge to the 7 + AA Barrage b/c there is that added small chance to abort two planes despite the need to target two different ones (usually this is going to be possible). Both have small chances of splashing 9 vital (3% for 7 dice, 7% for 8) so that is also a consideration, but again it is small.
I still really like AA Barrage, and it should be a boost in cost roughly equivalent with giving 8 AA. But it is not the be all and end all.
Torpedoes: This is like Gunnery, in that Mogami has a better natural line, but the SA of Chikuma gives it a better line overall.
Mogami: 3/3/2/1 Chikuma: 3/2/1/1 (4/3/2/2 with SA)
It is close, but maybe unlike the Scout Cruiser SA, when Chikuma is within torpedo range, she is probably going to be targeting a prime unit. Whereas, Mogami may be shooting at a lesser target than what it scouted.
Scout Cruiser 2 v. Scout Planes: Both help air and surface builds that use either gunnery or torps. But Scout Planes also helps sub builds. So that gives Scout Planes an immediate boost over Scout Cruiser--typically a greater impact.
Adding 1 torpedo also is usually a bigger impact than adding 1 gunnery dice, especially for longlance units.
E.g., 16 dice gunnery versus 9 armor / 15 vital. Hit = 76% chance; vital = 10%. Boost by one dice to 17, the percentages change to: Hit = 82%, vital = 15%.
The boost to a vital shot cannot be ignored for gunnery as at some dice numbers it may increase by over 10%, but overall those torps are going to be doing more for you, and in IJN builds, there are usually more decent torp shots that matter than gunnery shots that matter.
What Mogami is going to most likely do is mess with groupings a little. I may not put both my BBs or carriers in one sector.
The feeling I get is that Scout Cruiser 2 is probably relatively comparable to Scout Planes, but because of the added flexibility, especially for bomber builds, I may give the edge to SC2.
Overall: That was kind of rambling, but overall I think Mogami does come out ahead--mainly for the AA Barrage SA. But it is not by much, so a 1 point increase over Chikuma is probably all that is warranted. You can get the same Gunnery boost impact with two Gotlands at 20 points. There are some trade offs or advantages to that approach, but overall, the Mogami is probably a better bet.