does it come with the bait?

No bait included. I used a piece of cereal with peanut butter on it. I also dabbed the door with peanut butter as enticement. Don't use too much bait. A little bit will do. Mice can't vomit. If you load the trap up, it might not be so humane.

Used to use these and they worked everytime. Years later now with new cubes and this mouse is getting out after eating bait. How?

This particular trap worked for me about 2 months and then the mouse or mice figured out how to get out. I continued to bait the trap for a several more weeks. The mice would go in, eat the bait, and go out again. I could find nothing wrong with the trap and nothing stuck under the ramp. The trap had become a feeding station!! I went back to a 'wind up' live trap which I have used for years which mice can not get out of. The only reason I tried this trap was my wind up live trap was not functioning any more as the wind up mechanism would not stay set and spin down. I would have bought another one except the store only had this trap. The moral of this story is mice are smart and can get into almost anything and through such a small space you would think was impossible. If they can get in they most assuredly will try to find a way out. This trap unfortunately has a way out for the smart mice.

Are there air holes? I want the mouse to be able to breathe.

The swing door is designed to allow air. It does not seal and has holes drilled in it as well, so they would be able to breathe fine. The limiting factor is water. I strongly suggest checking the traps at least every 24 hours.

Is there a way to add additional ventilation holes without a drill? My drill is broken, and I like these, but want to make sure I can ventilate it.

You might try an ice pick but be careful not to jab yourself. The plastic is thin and brittle so it might be hard to force an ice pick through. I don't know why the manufacturer wouldn't put vent holes in it. We have been catching mice on a fairly regular basis but on more than one occasion the food has disappeared. We figured one mouse came in and got it and another mouse came along and opened the door and both escaped.