This refers to the the “Mariel Boatlift”, the real life event which was depicted in the beginning scene of the movie Scarface – where many Cubans immigrants fled to the US.

The Mariel boatlift was a mass emigration of Cubans who departed from Cuba’s Mariel Harbor for the United States between April 15 and October 31, 1980.
The event was precipitated by a sharp downturn in the Cuban economy which led to internal tensions on the island and a bid by up to 10,000 Cubans to gain asylum in the Peruvian embassy.

The Cuban government subsequently announced that anyone who wanted to leave could do so, and an exodus by boat started shortly afterward. The exodus was organized by Cuban-Americans with the agreement of Cuban president Fidel Castro. The exodus started to have negative political implications for U.S. president Jimmy Carter when it was discovered that a number of the exiles had been released from Cuban jails and mental health facilities. The Mariel boatlift was ended by mutual agreement between the two governments involved in October 1980. By that point, as many as 125,000 Cubans had made the journey to Florida.

Double entendre:
1) He’s rapping and loves to do that

2) Like a newlywed on a honeymoon, he’s having sex with (doing) the women he loves

DeSean Jackson is an NFL footballplayer known for burning past DBs (Defensive Backs) with his speed. He is a receiver and returner.

Raining on someone’s parade means being critical of something. P.O.S. is saying Doomtree is willing to be that critical voice that may wreck the party, but will speak truth and opposition to popular ideas. In a parade, large crowds gather around to watch floats and people march down main streets. There are often patriotic tinges to parades – celebrating the history of a country, the accomplishments of the country, and the country’s overall excellence. There are several acts of pretending involved:
1. participants go to great lengths to appear happy and excited
2. viewers are expected to be pleased and cheer
3. everyone is pretending that the country is what they are portraying it as, which involves self-deception as a nation. there is a disconnect between the reality and the nation’s mythical image.

Parades also have a militaristic feel as they are reminiscent of soldiers marching in lines. P.O.S. is saying that Doomtree, as a group, is going to cut through what he considers to be nationalistic, over-patriotic bullshit and be real. He’s also encouraging his listeners to rain on parades a.k.a. speak critically and honestly to misguided half-truths – he says Doomtree members are pro parade-rainers.

This line could also refer back to the line “They make it rain, rain, rain go away.” P.O.S. is contrasting what he and Doomtree are in favour of (making it rain on parades) with what other rap artists encourage (making it/money rain on women).

he has mentioned this a couple times such as in Lost Around the Way… you can also check this article out, recently put out where he speaks on a song on the RED album. look at the last “chapter”.

This is probably a biggie reference, “Fuck Bitches, Get Money” was a popular chant that biggie started during his rapping career.