When leveling an unborn reaper, if you can, turn the egg hatching rate to 0.01%. The time will go to just shy of 6 days. You'll have plenty of time to level. Once you get it to level 75, go back to your base and put the egg hatching rate to 6%. You'll have 12 minutes. Go to a confined area. Have a bed nearby. Don't have it in the area unless you want to die over and over again when it's born. It will kill both players and creatures when in the larva phase. Once it reaches the second phase its fine. Take it off wandering and it won't be a problem anymore.