I need a custom missile,but i not fast as hell

Let's look at a theoretical example I just made up which probably looks similar to yours:
In this case, the number "2" represents how many "tics" long each animation frame lasts for. The value for a tic is about 1/35th of a second. The lower the number, the faster the effect happens. So adding more tics to the Fire state will slow it down. You can do this by adding extra animation frames that don't do anything except pad out the animation sequence, or making existing frames take longer. Also, in this case, the function "A_FireCustomMissile" is applied to EVERY animation frame on the line (F, G, and H), not just the last one. So you'll get three fireballs in rapid sequence from one attack function. If you only want to attack once, make sure that your attack function is only applied for one animation frame.

Here's an example of something that can fire a projectile once every 1/2 of a second, which is probably closer to what you want: