[Principled]

"What brought me down was the rules....." Laboy said.

Should was be were?

Well, no. The subject of the sentence is the singular pronoun what. It does sound odd though.

It's like the correctly grammared sentence, "None of us speaks English well."

[Consort]

Well, no. The subject of the sentence is the singular pronoun what. It does sound odd though.

I think it can go both ways:

"In some cases, you can treat a clause with what as the subject as singular or plural, depending on the emphasis you want to convey. In What excite him most are money and power, the implication is that money and power are distinct elements; in What excites him most is money and power, the implication is that money and power are a single entity...,"

More info and examples are provided here.

[King Prout]

"None" is a contraction of "not one", so it is the "one" which necessitates the singular form of the verb.

"What" is not specifically singular, so the form of the verb would be determined by "the rules".
eg: "What were those things?"

Remember that a form of the verb "to be" sets up a verbal equation or direct comparison, and in this clause "the rules" and "what" are interchangeable elements.