The easiest place to get that trophy is on the first level, you can even get it on the first difficulty level.
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The first (?) item you get if by the time you got to the mid-stage boss – the three eyes – you have accumulated a big enough score. The score depends on the scoring mode as well as on the ship type.
The second (?) item will appear if you manage to kill all boxy X-shaped enemies before they reach the middle of the screen.
The third (?) item is obtained by point-blanking both of the two round-robot-like-looking enemies. The second one will drop the item.
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Note: For the first secret bonus I used the Reyka ship, and my score was about ~295.000 points in order to make kim appear. I was playing on the first difficulty level, with Original scoring mode.More informations about the other secrets:
And explanations from Rafael Lima (dev of the game) about the scoring (?) items:
Ok, let's go. I'll use your own Nina 1cc video as a reference, it's at
for anyone who cares :)
On every level there's a midboss that will spawn a secret item if you kill it making a good score on the level up to that point. The only thing that matters is the score on THAT level so far, it's not your score for the full run (and if I recall correctly, even continuing won't reset the curremt level score counter). Also be aware that the points you make by cancelling bullets when you kill that midboss will also count towards this, the check to see if you made enough points on that level is made after those points are added to your score.
For level 1 it's the eye midboss,
For level 2 is the core with the 2 helper bigger ships (you HAVE to destroy the bigger ships for this secret item to spawn, not just get a good score
For level 3, it's the midboss that sapwns that slowly moves at you at first, it's at 8:00 on the video.
For level 4 it's the big guy with the machine guns at each side, at 12:37
For level 5, it's the golden ship who fires bouncing shots, right before the midboss with the sidewalls
For level 6, it's the one with the arm cannons (You can destroy his arms for extra points, though it's possible to achieve the necessary score without doing it).
For level 7, it's the red midboss who spawns a lot of mini-laser bullets at 25:27 on the video.
So, recapitulating, you need to score well during the level before killing those bosses. The accurate number depends on the ship you are using, so just try to score as well as you can.