'is'. Although the sentence is in past tense, because the clause still holds true, 'is' should be used instead. Meaning, the person is still short-tempered. If you use 'was', it would mean that the person is no longer short-tempered. This is not what you meant to say. Some examples: A) If I were to fight someone, I would choose to fight someone who is small-sized. Note: 'were' and 'would' show that the sentence is in past tense, but because the person is still small-sized we use 'is'. B) Jane, who is the director of Taste Inc, was my girlfriend in college. Note: Jane is still the director so we use 'is' but no longer my girlfriend so we use 'was'. Feel free to ask if you don't understand anything. On a side note, it should be 'any problems' instead of 'any problem'. We always use the plural form of the word after 'any'. Example: Do you have any cigarettes?

was 2nd conditional Remember, the "someone" is hypothetical (imaginary).

was, because "came" refers to past tense, so "was" should also be past tense, where "is" is present tense. A.

Yes, it's a second conditional pattern: if....(past simple tense), then ...would (action).

the 'short-tempered' here acts as an adjective and a subject compliment to the pronoun 'someone'. therefore, I suggest you use 'is'. if you're confused still, try simplifying your sentence. "if ever I came across a short-tempered guy..." :)