[quote:footjzyp]I remember reading something somewhere saying that Construct has an unlimited amount of actives available and without any slow-down, is this true?
Depending on what graphics card you have, and what you're doing with the sprites, you could have several hundred sprites moving around on the screen without any slowdown.
Physics will slow things down with hundreds of objects colliding at once, because it's mathematically CPU intensive. As will calculating collision between normal sprites several hundred times per tick (as in with a loop).
Heavy use of shaders, motion blur, large amounts of particles, etc. will cause slowdown on some graphics cards because they're very GPU intensive. The Plasma object will as well for some people. Be frugal with your effects. Try to fake it as much as you can by creating effects on your sprites before importing them into Construct whenever you're able to.