What type of game can be taken with
a crossbow pistol and how close do
I have to be? any other tips will help.

Squirrel and rabbit sized game for a 50# pistol. Range would be around 10-15 yards or so. I used to have one like that.

Check your local game laws, probably not legal. The ones I've seen were remarkably unimpressive for any kind of hunting.

i wouldn even take it out

Just a very old rule of thumb, and probably not applicable across the board any more, but a decent enough way to compare relative power with a conventional bow... Take the crossbow's draw weight and divide by 3. That will give you a rough relative power comparison. That 50 pound crossbow pistol would be roughly equivalent to a 17 pound draw bow, and probably less due to the extremely short power stroke.

I know I killed many rabbits with very low draw weight bows when I was a tyke roaming around grampa's truck garden. But that was half a century ago, a different time with different views on hunting and ethics.

And as mentioned, you have to look beyond the low power to the legalities. In Texas, it's not legal to hunt with a crossbow less than 125 lbs draw or with a stock less than 25" long. So definitely check your state regs.