Does smoking mary j actually kill brain cell or does it paralizes them like make them not work for awhile.?

No. There is no evidence that marijuana "kills" brain cells, but heavy marijuana smoking is associated with loss of intelligence over time, and does effect the ability of the brain to learn, as well as reducing the ability to memorize. This occurs with high-dose and regular use, and some people are more susceptible to these effects than others are.
Yes. Mj is a well known cause of psychosis and decreased memory. Students who use mj consistently score lower than those who do not.