If you do the logic in the correct order it should be fine :
Box : spawn crystal. set cystal.variable to box.variable
On box destroyed : pick all crystals where crystal.variable=box.variable, destroy crystal
Main problem is event 21, which is pretty much always true and sets the animation to stand which is going to interfere with other animations.
Take out the key press. If it's a system that must be switched on with Q but then lock on constantly, toggle a boolean on and off with Q. Then use a condition if bool=true for the lock on logic.
Post a screen of the events or share the C3 file
You give the box an instance variable, some kind of ID number. Then when it spawns the crystal you assign this ID to the crystal also as an instance variable. So box.ID=crystal.ID, they will be the same number. Then when box dies, you say pick all crystal where crystal.ID=box.ID and destroy crystal.
Checkbox button 'is checked' : set start button enabled
What's the area limit? It's set position to random(low,high), random(low,high) for x,y.
Give the monsters and items Persist behaviour, more here : construct.net/en/make-games/manuals/construct-3/behavior-reference/persist
Your UI and Game layers are the wrong way round in Layers bar. Drag them so UI is 1 and not 0.
oh! so it was Angle of Motion?
hmm, see first response on the thread...
The bullet does not get destroyed unless you tell it to be destroyed, so it's fine?
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It's not possible to help with this without seeing the file or at least a screenshot of your events.
Looking good, but possible FPS issues there?
What you're looking to use is 'set bullet angle of motion' instead of 'set angle'. I assume you bumped up the speed on the balls which don't have stepping. 1500 speed is good for the ballstep objects.
Just saying you may have saved it on a beta on one device and now you are on stable, what version is it showing? I didn't see that error before so I am just going off that. You can bring Ashley to the post, he might be able to recover something. Also it's a full game and you don't have back ups?