Resogun is an enigma. It tasks you with many goals - save the last humans, beat the level, keep up your multiplier - but it's not always clear what to focus on to topple the leaderboards. The game itself suggests that the multiplier is your main priority to achieve a high rank, and it is, but that's only scratching the surface.
To help aspiring Resogunners up their game, the jedi masters at PlayStation Access have created a 15 minute video demonstrating how to achieve a 100 million-plus score on the Experienced difficulty of Housemarque's delightful PS4 launch title.
First things first: You don't need to save the humans, despite the narrator telling you at the beginning of every stage to "save the last humans." It helps to save them, of course, but if you really want to go for the big score you'll want to wait until all the humans are free and save them in very quick succession, as is done a minute into this video. Granted this is a very difficult to pull off pro strategy, but it's something to aim for anyway.
As far as the all-important-multiplier is concerned, there are ways to keep this in play you might not have realised. Picking up a human, taking them to an extraction point, and shooting the barrier off a power-up, all contribute to preventing your multiplier from expiring. Another seemingly counterproductive way to keep your multiplier from restarting is to use a bomb. It may go against every instinct you have to keep these things until you're in a tight spot, but is being alive with a rubbish score really living? I thought not.
Other tips: Boosting through enemies is vital as slaying foes in quick succession garners more points, which is something the game never tells you. The longer you boost the bigger the explosion radius of you coming out of it is, but it's still best to use short, controlled boosts so you don't get in a sticky situation with it uncharged. Boosting is also handy for throwing humans further. It takes a bit of practice, but I've found this to be really useful in Master difficulty where there's only one extraction point per stage.
Since the game greatly rewards you for how quickly you slay foes, the time-slowing Overdrive mode is absolutely crucial as you can take out a ton of enemies in what the game considers to be a very short time. Apparently a really well executed use of Overdrive can net somewhere in the neighborhood of 20 million points.
Because Overdrive is so incredibly important, PlayStation Access recommends using Phobos, the slower, more powerful ship with a longer-lasting Overdrive. Its main weapon fires less frequently, but does more damage too.
There's some other secret tricks to Overdrive. When you hold R1 down you'll see a white ring appear around your ship and contract into it like a QTE in Castlevania: Lords of Shadow. Release R1 when the white circle is within the parameters of your boost and Overdrive meters but before it hits your ship and you'll release a large burst in addition to your regular Overdrive.
Additionally, while you can't use Overdrive in short spurts, you can boost during it, which pauses the Overdrive until you stop boosting and it will resume where you left off. This is incredibly useful for taking out two different clusters of enemies on opposite sides of the map.
On that note, it's recommended not to save Overdrive for bosses, even if it makes them a lot easier. There is one exception to this, however: the third boss. A giant cube that breaks into smaller cubes, you can score big using Overdrive against the nefarious geometric shape and the bits it sheds.
It's a lot to take in and I'm sure more strategies have yet to be revealed. But ultimately practice makes perfect, so go out there and watch these new suggestions slowly but surely raise your score. Good luck!