Master of Arms is pretty much a second Shield skill for most gladiators, something like an insurance that if you need to swap weapons you won't have to retrain. Theoretically it can be a good skill if you know all of your opponents in advance and fight rarely, something like Blood Games extended to all other modes but otherwise nobody really changes weapons except when something is tested for the sake of the testing. The War class doesn't have attack-neutral styles like Berserk or Counter Attack so you can't equip a sword and a hammer at the same time with good effect. Still, the skill can remain unchanged - it's nothing exceptionally useful but it's not bad either.

Iron Jaw is... don't know what it is. I really hated it a while ago when I had it on a hybrid War who got stunned pretty much as regularly as the other gladiators I had at that time (without that skill of course) and the KO reductions weren't all that noticeable either. Recently I decided to give it a second chance on Toros and, again, I'm not impressed with that skill. Getting stunned three times in one fight isn't really my idea of "protection" so I'll just ignore it on the future builds.

War Cry does damage more consistently than Barreling Attack when used with one-handed weapons and less consistently when used with 2H weapons. The chance to trigger stun is really, I mean REALLY small, something like 1 in each 10 attempts and I haven't noticed any bonus damage compared to a standard attack like Aboede. The problem I have with that skill is the fact that it can single-handedly cause the defeat of your fighter if you are unlucky with the dice rolls. I've had cases where my War wouldn't deal any damage for 3 or 4 War Cry attempts (all or most of them resisted by the opponent) which the opponent liked very much. No other skill in the game can so counter-productive, even Barreling Attack always deals damage at lvl 10 when used with a 2H weapon or always knocks down the opponent when used with an one-handed weapon, you are not gambling with your fighter's efficiency when you pick it.

Down and Dangerous... so far only oedi seems to like it, although his gladiator (1131) doesn't seem to share his opinion. I'd give the skill the benefit of doubt until I see it on a fully equipped gladiator. I'm not planning to use it on any fighter until then, Armoured Fortress is vastly superior to it at this point.

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A footnote - the War class needs the most attention in order to be efficient but it can also really dominate the arena if handled properly. The only "lazy" War build that exists currently is the shield-bearing tank - nothing complex about its strategy or equipment requirements - but all other War builds need you to plan ahead a lot of things and play with the strategy quite a bit until you find the optimal approach. That's what makes the class so interesting though. When you find the right combination of strategy, equipment and skills, it's quite rewarding.