Boss Upgrades are BCG's plan to keep this kind of thing from happening. They do a decent job of it, but it could have been better. Their biggest issue is that a few have effects that only trigger at the beginning of their turn, which, when they're being focus fired, can mean going multiple PC attacks without the defensive buffs that the Upgrade should be giving them.
I'm going to count how many of those there are while doing the rest of the review.
This is quite the powerful defensive effect. An extra 5 Defense is fine but an extra 10 Defense is near-unbeatable against an unprepared PC Squad. Most optimized units use Beams or non-Beams exclusively, not both, so either option makes for a good weak point. The 'pattern shift' effect can be optimized by switching to the specialization of a PC that has already been defeated by the time the Boss hits its 4th Threshold Level. With all that said, even if the PCs can't naturally play around the ability, a few of them should have ways to ignore Active Defenses anyway, keeping this from being unbeatable. Adaptive Morphology is based on the 'elemental barrier' abilities that some bosses get in JRPGs, making themselves immune to all but one element and cycling through them as the battle goes. It is more of a fantasy videogame genre convention than a science fiction anime convention, but I think it still works. Delayed Defensive Upgrade Count: 1.
Afterimages is great. It makes use of a good mechanic that doesn't get a lot of love (Disadvantages), is quite strong but not strong enough you can't punch through it; And you don't even have to wait for the Boss' own turn to start using it. If the Boss is being focus fired (which they probably are) then they can use this right away. This is probably my favorite defensive Boss Upgrade.
This one seems kind of weak at first, because it only works against a single target... In theory. As written, it also works against PCs that are in a Duel with NPCs, which means you can make a very nasty encounter with lots of melee Grunts and give the boss this + Tentacle Lash + Whirling Death to do absurd amounts of Damage. It is borderline unfair. I would have preferred if this ended up being strong the old fashioned way instead of being weak when not being optimized to hell and back, but I'll take it. This is a half offensive, half defensive Upgrade, and the part that we care about is the offensive one, but its defensive bonus does take some time to come online. Upgrade Delayed Defensive Upgrade Count: 2.
One of the best Boss Upgrades in terms of raw power, doing about 25 Damage to at least two PCs if you use Not So Fast to assist with the repositioning when being attacked! It might seem overpowered, but the investment in Systems means that the Boss probably lacks the Might/Guard to attack and defend the traditional way, so an ability like this is necessary. It is devastating at how PLs when PCs still have low threshold totals and still lack the Genre Powers and Active Defenses to withstand an attack like this or the reach and mobility to stay out of its area of effect. At higher PLs, PCs tend to have those things and can mitigate or avoid the damage trigger, making it still dangerous but much more manageable.
It Keeps Coming Back
Probably the most powerful defensive Boss Upgrade. Even assuming a worst case scenario where the Boss is being focus fired and could die in a single round, the Level 4 ability will negate death and fully heal that last Threshold Level. If the Boss had 1 Threshold left and took 50 Damage? It still lives with its last Threshold Level full. That's really good! The L2 and L3 abilities are just okay, but considering how great the L4 ability is, the extra healing there is just gravy. Obviously, this isn't very good with Bosses that have a Threshold Attribute of 5 or under. With a Threshold Attribute of 10 and a single activation of the L3 ability, this heals for 15. Let's say the defeat negation effect counts for 5 more points of Damage, and that leaves us at 20 extra health. That's 50% bonus HP, which is a very healthy amount of extra endurance... And that's assuming the base regeneration effect doesn't trigger multiple times! This is a scary ability, fitting for the regenerating supermonsters that the genre loves so much. Delayed Defensive Upgrade Count: 3.
This is the other candidate for most powerful defensive Boss Upgrade. Nanoskin Shell used to protect the Boss for a static value regardless of PL. At first that was 15, which was useless at high PLs. After that it was 30, which was fine at PL 5 but overwhelming at PL 1. Eventually, I made PL part of the formula and this became the first ability that used PLs for its mechanics. There's still very few of those and the territory is largely unexplored, with Nanoskin Shell being probably the best applied of the bunch. Comparing it to IKCB (the above Boss Upgrade), it is more reliable against optimized parties but doesn't have the potential to make the Boss near unbeatable with constant regeneration. It is a very close race between the both of them and I would give it to IKCB, but not for much and not for all Boss builds. Clearly, this means that supertank Bosses should get both instead of just one.
Phantom Predator is very powerful but also very susceptible to debuffs. Either you can drain the Boss of Energy or debuff their Speed (assuming they don't use Systems), or you have to push through 8-10 extra Defense with each attack. It is possible to build around debuffs by having 10 Energy and using Systems instead of Speed, but that's taking MP away from more generally useful Attributes. It is a little too binary for my liking, but it is one of the more useful abilities for pushing PC Squads to the limit. I would be more negative of it if it was available to PCs. But as a NPC-only thing that is not supposed to be repeated often, I think it's fine. The name is a reference to the Predator, by the way. Delayed Defensive Upgrade Count: 4.
Three Times Faster
Three Times Faster, possibly the most famous Mecha meme of all time, is on a surface reading a tweak on Bloodlust. Take a second look and you realize that it is probably better than Bloodlust, because you don't have to be Dueling the target for its benefits and this goes perfectly with a kiting Hypersonic Striker build. Should you dig even deeper, though, you'll find that Speed debuffs pretty much kill such builds and Bloodlust can be exploited as has been pointed above, making Bloodlust better than TTF when optimizing Operations around it. Delayed Defensive Upgrade Count: 5.
We are Many (Specialist)
Big bads that spawn lesser bads are a videogame staple that happens to work really well in a game like this. This take in particular lets you craft a lot of interesting Operations. You can do a lot with six PL 0 Grunts, and while having minions spawn endlessly every other fight could get old, the many ways you can build them should keep things relatively fresh. It is also extremely powerful when optimized, because six glass cannons that are guaranteed to spawn after Tension has already gone up a point or two make Weapons like Resonance Cannon and Incinerator even more dangerous than usual when in the hands of Grunts.
That's 5 Upgrades that, in hindsight, should have been effects that happen immediately, grant offensive buffs, or have defensive effects that can be used without delay... At least in theory. I'm not quite sure how to make a regeneration effect for IKCB that triggers immediately but isn't just Nanoskin Shell with different wording. It would also break the symmetry that the half offensive half defensive Upgrades have going for them, though the offensive bonus could also apply immediately to fix that I guess.
Another problem they have is that some of these are so powerful they're borderline broken and multiple Bosses with them at the same time would likely provoke a TPK. It's dangerous to have too many abilities like that in the game, but Bosses have a lot of trouble handling 2 PCs on their own otherwise, let alone 4 or more. Like with Grunts, many things about Bosses rely on implicitly trusting GM's to not purposefully design unwinnable scenarios. It is not easy to optimize your Bosses by accident to the point where they can do that, thankfully. It's not my favorite kind of approach, but I'll take a game that is accidentally too hard every now and then over one that is almost always too easy.
Overall, I think these are a step in the right direction for tabletop RPG boss monsters. It's not quite as dynamic as bosses having multiple forms that all play differently, because all the Boss Upgrades do is strengthen the same ability the longer the battle goes. It's still better than the usual, though.
I would like to figure out a way to codify multiple forms into a single Boss someday, though it may take so much space and be so complex that the end result may not be practical.
Next: Boss Weapons.