Back in the day mighty blow used to add one to both your armour and injury rolls any time you hit someone. Now it only works on blocks, and you can only use one of the +1s, not both. So you only get the injury bonus if you would have penetrated their armour without the mighty blow bonus. Those seem like reasonable nerfs, but what does it end up coming in at power-wise?
Once again it depends on the starting armour of the player hit. I'm going to ignore what it takes to knock the guy over in the first place and just look at the end result if they happen to get knocked down. There are two relevant numbers, I think... Odds of getting at least a KO (important for thugging teams that need a clearer field to score in the second half) and odds of actually inflicting a casualty (important for leveling up, clearing the field, and inflicting permanent damage on the enemy).
Those are actually some pretty substantial gains! You more than double your odds of both KOing or casualtying an orc. The percentage boost isn't as big against an elf but the raw increase is even bigger. I guess if I'd stopped to really think about it I should have expected it to be such a big deal. You're only adding 1, but it's a pretty relevant one. Expanding the casualty range from 10-12 to 9-12 takes your hits from 6 in 36 to 10 in 36 alone! Then when you consider that you're adding a whole armour band in at 6 in 36 and you can see where the gains are coming from. Heck, on the armour 10 dudes that extra band is as big as the old one alone! (3 in 36 of rolling a 10 versus 3 in 36 of rolling 11 or 12.)
I'm now questioning how many guards I've taken on my dwarves... The linemen should have it first, but I also put it onto my troll slayers (who both remain level 2) and probably should have gone with mighty blow there. Especially since with dauntless they tend to go after the high armour targets and the odds of taking one of those out really go up with mighty blow. I was thinking my dwarves were done getting ready for the league (there's an initial salary cap) but I think it might be worth trying to squeeze out another level or two on some guys and pick up some mighty blows.
What about finding a team that starts with a bunch of mighty blow? That could be useful...
Goblins have 2 trolls.
Halflings have 2 trees.
Ogres have 6 ogres.
Orcs have 1 troll.
Skaven have 1 rat ogre.
Undead have 2 mummys.
Wood elves have 1 tree.
Most of these teams have mostly terrible dudes (goblins, halflings, and snotlings are all strength 1 or 2) or can only get 1 guy with drawbacks along with mighty blow. I kinda want to try ogres out even though they have truly terrible snotlings who only have 1 strength and don't have tackle zones for dodging. Having 6 big dudes with mighty blow could be a real problem for limited roster teams to deal with.
Another thing to consider is teams that can pick up mighty blow on lots of dudes thanks to having access to strength skills. Chaos and dwarves are the only two with pretty much full strength access. Nurgle teams have 9 dudes who can access strength skills which is pretty good, though they all need to pick up block as well. Really, dwarves seem like the way to go. If only they were better at playing football!