In the “Bitch Don’t Kill My Vibe” music video, the string ensemble that plays during the outro is cut off with a black shot with the text: Death to Molly.

Molly is the purest form of ecstasy, usually given as a free powder or contained in a capsule.
Taking molly has many affects on different people, it is a drug that hits the off switch on your brain, which could a good thing or a bad thing, depending on who you are.
Molly is consistently mentioned in contemporary rap, be it most humorously referenced by Trinidad James in the legendary:
Popped a Molly I’m sweating (woo!)
However it has also got artists in hot water, on Rocko’s “U.O.E.N.O.”, which features rapper Rick Ross, in which he rhymes:
Put Molly all in her champagne, she ain’t even know it
I took her home and I enjoyed that, she ain’t even know it"
Ross, who also remixed this Kendrick classic, has had his endorsement deal with Reebok dropped as as result of these lyrics.
As of yet, it is hard to tell if this is what Kendrick ominously demands dead, but it can be easily interpreted as a kind of rallying call to take drugs seriously and make sure it is not promoted through Hip-Hop, something Kendrick clearly takes very seriously.