You can unleash havoc. Not sure what you're talking about silly blondie. ;oP

true, but there's only a few usages. wreak is singular i think

it's a verb... can't be singular or plural

singular in its usage i mean. it's only ever used in combination with one other word

it definitely isn't *exclusively* singular. and it's pretty safe to say that "wrought havoc" or "wreak[ed] havoc" is a snatch from some literary prose i'm unaware of and people just used that way ...