No, "Florida-based developer Nick Mastroianni II has [not] assumed the Coliseum’s lease" (updated/clarified)

From Newsday, 10/28/20, New York Riptide plans to play its second NLL season at Nassau Coliseum

The COVID-19 pandemic has thrown the future of Nassau Coliseum in flux. But a second team besides the Islanders is confident it will play its next season in the venerable barn.
The New York Riptide of the National Lacrosse League announced on Wednesday the franchise’s second season would begin in April with the goal of playing home games at the Coliseum.
...Florida-based developer Nick Mastroianni II has assumed the Coliseum’s lease after Mikhail Prokhorov’s Onexim announced in June it was shutting the building.

Newsday keeps describing Mastroianni that way, but it's partly imprecise, partly dead wrong. 

Yes, he's been a developer but his main identity is a founder/operator of a "regional center" called the U.S. Immigration Fund, a private entity that serves as a middleman, recruiting immigrant investors who offer low-interest loans to real-estate projects in exchange for green cards, under the federal government's EB-5 program.

So neither he nor a company he owns could have assumed the lease. Rather, a special-purpose entity consisting of EB-5 investors, with him as manager, assumed the lease. But since he controls information and reaps fees from that entity, he's a key player.

Well, 200 immigrant investors offered the loan, but it's not clear why Mastroianni would take over the debt. He served as manager of the company offering the loan, and also runs the biggest and busiest "regional center"--a middleman loan packager for EB-5 investors--in the country. If he gets the lease, it's because he now controls the loan--nice work for someone who put no money up.

The Times repeats its mistake language

A 10/21/20 article in the New York Times, After Delay, Ticket Holders Are Getting Refunds for Two Concerts, explains that Mikhail Prokhorov's Onexim is finally ensuring refunds to ticket-holders for two canceled concerts at the Nassau Coliseum.

Onexim walked away from the lease earlier this year and, as the Times put it, "the county negotiated a transfer of the lease to a real estate developer that had helped finance renovations to the arena."

That may be accurate, but it collapses what strikes me as an astonishing negotiation. (Updated 12/1/20.)

Actually, no. The lease is controlled by a special-purpose entity representing the immigrant investors under the EB-5 program, as I pointed out previously in response to the previous Times article on the issue, and the "real estate developer"--and affiliate of the U.S. Immigration Fund--is the middleman that has no ownership but reaps fees.