Fear and Certamen

In our Saga our group is being coerced by a more powerful NPC mage into dealing with some spider-themed hobgoblins. The rumour is that this mage is arachnophobic.

This leads to the following question:
Is it possible to take advantage of this Fear in Certamen, and if so, how?
I am thinking that a Certamen with the Technique of Animal might involve phantasms of spiders if my character so chose, but is it only a modifier of +/-3?

With a technique of Animal (for actual spiders) or Imaginem (for illusions of spiders) you could benefit. I don't think they apply a -3 to their totals - instead you can use their fear to force them to make a concentration roll with a -3 penalty due to their fear. See ArM5 p90 certamen rules, where it lists the three ways to win - "The third way to win certamen is to maintain concentration in the face of distraction when your opponent does not". This does not necessarily declare you the victor though, so trying to win through psychological tricks may not work.

Everything darkwing said, but I would add that their rolls would be modified by their personality traits, rather than a flat +/-3. We have always house ruled that Personality Flaws (such as Fear Spiders) add to or modify personality traits, I believe we made it +1/+3 for Minot Major, but have to check.

This means that if a character had Brave -1 or Fearful -2 (or the like) a Major Fear Flaw (for spider) would make that Brave -4 (spiders) or Fearful -5 (spiders).

In addition, I might allow the PC magus in this case to use Finesse to make the Certamen more frightening.

A silly question.
Are the phantasms produced in Certamen merely a visual phenomenon, or do they also affect other senses?

According to Ars Magica 2nd edition p69 "These illusions can affect all the senses and are visible to all" (5th edition doesn't seem to say)

I believe one of the Tremere techniques involves fear . . . the chariot? But I don't recall how this works mechanically.