What word means a “male temptress”?

Solution 1:

-ess is, in fact, a feminine suffix. The male or neuter form (English tends to conflate the two) would be tempter. As a note, the title The Tempter, with capital letters, is given to the Devil.

A person who tempts in a sexual fashion might be called a seducer (seductress if female).

Solution 2:

A mythological creature called succubus is described as the ultimate temptress, using sexual seduction to lure its prey. The male counterpart, incubus, similarly uses sexual seduction to lure in prey. These terms can be used to describe seductive people whose ultimate goal is self-serving or else makes no consideration for the wellbeing of the person being seduced.

Similar mythological creatures with less sexual overtones include sirens and will-o-wisps. These are less about seducing and more about distracting or enchanting their prey, but you could still use these terms to suggest the meaning you're looking for.

Solution 3:

                    Temptress / Feminine; Tempter / Masculine

OP also requests a description of "a man who entices others into making bad decisions"

Such an individual is sometimes referred to as a “Svengali”

svengali n.: A person who manipulates or controls another, especially by force of personality for malicious purposes. See, the Free Dictionary svengali

Solution 4:

If you mean bad financial or professional decisions, the word you're looking for might be charlatan:

A person practising quackery or some similar confidence trick in order to obtain money, fame or other advantages via some form of pretense or deception. (Wikipedia)

A similar word is huckster: