This deer's extra antler is easily explained.
During a struggle with another deer to establish relative superiority and gain mating rights, the other deer embedded one of HIS tines into the unicorn's skull. That tine broke off and remains to be seen, for the amusement and edification of BB readers everywhere. Case solved.

I take issue with carnivorous hypocrites, who gladly eat meat from animals raised under restrictive factory-farm conditions by treacherous farmers, who then deliver them to uncaring animal executioners, who in turn hand them off to mind-numbed, underpaid meat processors, where the requisite amount of insect parts, rodent hairs and, you know, 'your basic filth' (to quote George Carlin), is added.

To their ignorant minds, this is somehow better than taking part in nature's plan, swiftly killing an animal that ran free and ate natural food all its life, then dressing it out yourself, taking the care appropriate for food that you intend to eat yourself.

Steve