There are some genre conventions that, when converted to abilities, only make sense having a downside to go with their upside. The most obvious example are aquatic Mecha, which should outperform others in the water but underperform while on land. Features and their ilk could have costed MP and they could have had a stronger upside, but I think they're best this way. Not costing MP means they are easier to work into a build at low Power Levels, which is ideal for L0 Grunts. It also means the upsides and downsides have to be on equal footing, which is more a matter of aesthetics than one of pure rules, but it is nice all the same.
One thing that jumps at me from the description of Features is that the description for which ones should and should not be combined are very vague. The book takes for granted everyone will be aware that Flyer and Terrain Specialist (Land) is a combination that makes no sense and should not be allowed, but I've been asked by GMs how to challenge super-optimized PCs with this combination of Features. If I'd known, I would have made a sidebar on the subject.
Base units can represent either mobile battleships like those seen in Gundam, Nadesico or Yamato or stationary fortresses like those in... Nearly every super robot show there is. Special mention goes to Evangelion, which had the whole city of Neo Tokyo-3 contributing to the battles with tons of support structures. Base Units can harbor PCs inside, protecting them from harm and allowing them to switch Frames. The downside to having one of them around is that their destruction is a mission failure condition. I think this is a decent execution of the concept: You have a VIP Unit that is just as capable as everyone else's and provides some utility value, but can be overwhelmed like any other PC and thus must be protected.
The utility value of Docking can be a good way for PCs to avoid taking Damage for the first few Rounds while Tension builds up. Docked Units can even contribute to the battle and attack by exposing themselves to area attacks. Obviously, this needs the Base Unit to be bulky enough to withstand enough fire for at least 2 PCs and preferably mobile enough to avoid unfavorable Terrain conditions. The payoff is that when 2 or more PCs come out at full power they will make short work of the enemy while the Base Unit licks its wounds. It's risky, but when it works it does so very well.
The consequences of having your base unit destroyed are sidebar suggestions instead of having any concrete rules effect other than "you lose". On one hand that's kind of lazy, but one the other hand the rules effect being "You lost, now deal with the consequences." is much more effective than any kind of rules-based penalty. The combat is a vehicle for cool storytelling, after all. I suppose the sidebar could have been one or more pages of detailed suggestions but, at the time, that effort was better spent elsewhere.
This is the Feature with the most impact. Halving all non-Might Test Damage is HUGE, but so is losing half your Energy. Some of the most dangerous Grunts will now be half as effective as they usually would be, Rivals will have several abilities be made near-useless and the most powerful Boss builds will be rendered to flailing helplessly this way. You're just as vulnerable to raw Might Tests as anyone else and having 2-4 less Energy to play with will make enduring super attacks much harder.
It's honestly kind of OP. You can combine it with Internal Fortification to cover your weakness to Might Tests and you're super durable at the cost of having a 2-3 Energy build. You can also make it part of a Transformation, using up all your energy at the beginning of your Turn, then switching to your Extreme Fortification form. Next Turn you'll be forced to start with half your Energy before you can do any tricks, but if you switch to another form you can repeat the energy trick your next Turn. It's kind of silly and tells me that maybe the drawback should have been something else, but I'm not sure what it could have been.
Flyer and Terrain Specialist
These are the two most common Features. I just spoke about them two weeks ago when talking about Alternate Forms so I won't repeat myself. The other benefit about them is that they let the GM create non-mech enemies like planes/submarines/tanks which will behave differently from mechs at no MP Cost. This is very important for Bosses, who can technically be given regular Upgrades in place of Boss Upgrades, but you really shouldn't do that.
Power Suit is an alternative Antimaim. It costs no MP (obviously) but makes it so that, instead of losing Upgrades and Weapons, you lose stats when Maimed. Whether the effect is easier or harsher on the user depends on the build. Personally, I like these as a 'cleaner' implementation of the Maim rules, though they do loses some of the flavorful touch that the standard rules have to them.
While we're on the subject of Maiming, I'm glad you guys also like the mechanic! I'm still a bit conflicted over the rules, but I'm relieved that sticking with them was the right call. The poll between deep combat and streamlined narrative is much closer, but it didn't start that way. At the beginning, deep combat was winning by a landslide. Later on, streamlined narrative and neither/unsure got a lot more votes, which I found an interesting twist.
There'll be a new poll next week when we talk about Weapons.
Next: Default Weapons & Weapon Keywords.