Mobility Upgrades are thematically but not mechanically related to each other, they're linked by having similar flavor but their mechanics are independent. They could have been internal upgrades, but they make more sense as external upgrades. Plus, making them external let me lower their MP/Energy costs, to counterbalance that they can be maimed.
This used to cost 1 energy and 5 MP. Suffice to say, it was an autoinclude on waaaay too many builds for my liking then. Now? Perhaps it is a bit on the costly side, but every time you dodge extreme terrain with it is worth the cost. One thing I like about Antigravity is that it doesn't say "You can fly." then tells you to flip to a different page explaining how flight works. Rather, it (and all the other flight-granting mecha abilities) tell you what flight means. In this system, flight means ignoring cover and ignoring terrain under you. Very simple! In saving 3d movement for a sidebar, it keeps things rather compact. There is still one problem though: It doesn't say it can't fly over Impassable Terrain! It does say it ignores Terrain under you, but you can't move into a Zone of Impassable Terrain first to ignore it, so it is kind of confusing. It probably should have added "Can't fly over Impassable Terrain" in reminder text at the end. The underwater/space part of the text is there to remind GMs that they can make their own terrain properties and treat them however they want, and that sometimes saying "This terrain doesn't like this upgrade/weapon" is okay.
This used to be a 2/4 Zones boost, now it uses the same numbers Custom Defense does but for movement instead of defense. It wasn't a particularly necessary buff, but I liked the parallel and doing it didn't break anything. Also, the odd number makes Boosted Lance users want to take Gotta Go Fast to move a total of 10 Zones + Speed and get a juicy damage bonus. I like that this is a viable alternative to base speed bonuses for builds with a ton of energy.
When I made Slippery Chassis into an internal upgrade, I also considered doing the same with Reversible Thrusters. I ended up keeping it external just to make kiting less of an autowin for the higher speed builds that can pull it off - doing some damage to them should at least present the risk of forcing them to fight head on. As a maimable 10-point upgrade, this is useful for its intended builds, but often in playtesting it wasn't quite worth the cost for anybody but the most dedicated of snipers. There were some variants, but this turned out to be the least abusive of them all while still being playable. Considering kiting as a strategy is kind of abusive by purpose, I suppose that means this turned out well enough.
So this is a bit of a short post, because these don't have much of a story to them and they're pretty clear-cut. I do have a lot more to say about next week's subject though!
Next: Support Upgrades.