Hi there... 
Black hat SEO is unethical practice as well as a short-term solution to a long-lasting problem of a website for which a site runs the risk of being penalized by the search engines.
List of some common black hat techniques are :
?Keyword Stuffing
?Invisible Text
?Doorway Pages
?Artificial Traffic
?Link Farms
?Duplicate contents
Add if you have more information?
Black hat SEO is unethical practice as well as a short-term solution to a long-lasting problem of a website for which a site runs the risk of being penalized by the search engines.
List of some common black hat techniques are :
?Keyword Stuffing
?Invisible Text
?Doorway Pages
?Artificial Traffic
?Link Farms
?Duplicate contents
Add if you have more information?