botch dice in Certamen

Just checking.
Characters normally only roll a single botch dice if it happens in Certamen.

Except for the cases:

  1. character used vis that round.
  2. are in a foreign aura.

Sounds quite reasonable. I figure if there were more botch dice, then there would be a chance of Twighlight and Certamen wouldn't be accepted by elderly magi, who have more votes.

TMK it is only in the Rhine Tribunal, that 'elderly magi' have more votes in Tribunal. But in the Rhine Tribunal you automatically win any issue before a Certamen even can begin against a magus with less vote than you.

(I am away from books and very busy)

How about House Tremere? And for these issues alone, that would mean the elder half of the magi in the Order have more than half the votes.

My point is that putting yourself at substantial risk, maybe even of Final Twilight, makes Certamen pointless as a safe way to do combat. If it's safe, you don't have that substantial risk.

Exceptional circumstances might generate additional botch dice, for example if a third party interferes during the duel.

that is true.
One of the ways to be defeated at Certamen is to lose concentration.

Well, no. Obviously, there is the possibility of additional botch dice in "tricky" circumstances (say, when a friend of your opponent is magically tickling you, or when you are using a half-learned style).

But for vis and (foreign) auras, I don't think it's at all obvious that extra botch dice should apply.

For vis, in particular, it's never stated that additional botch dice apply. For other vis uses (spellcasting, studying arts from vis) botch dice resulting from vis are always specified. This suggests that there are no extra botch dice "by default" for using vis in certamen, or they would be explicitly stated. Of course, the SG/troupe is always free to add them (say, if you are flinging in a rook of infernal vis), but even then, the exact amount should be chosen adhoc, rather than at 1die/pawn.

For auras it's trickier. The extra botch dice apply to "supernatural acts" in the foreign aura, according to the Table on p.183. But the table specifies the only rolls/totals affected are Magic Resistance, Penetration, Lab Totals, Spellcasting and (Supernatural) ability rolls. Now, Certamen rolls are neither spellcasting, nor supernatural ability rolls. So the foreign aura penalties should not apply (again, except in an adhoc fashion, by explicit choice of the SG/troupe -- see above); in this sense, I would probably view the certamen rolls as rolls to "control" a supernatural ability that's already been invoked, very much like Finesse or Concentration (or Stamina etc.) rolls for spells that require those types of rolls.

For the same reason, I would argue that you gain no warping from botching Certamen, unless in exceptional circumstances (again, see above), because you gain 1 warping point per botch only when invoking a supernatural effect. And you are invoking a supernatural effect only when creating your phantasm, not every time it thrusts or dodges.

Note that this reading of the rules, which I believe is the strict literal reading, also makes a lot of sense "in practice". Otherwise, practicing certamen even under the best circumstances would involve gaining one warping point every 50 rounds (remember, you roll twice per round, attack and defense) i.e. every 5 minutes of certamen. Practicing for a week, at a leisurely 4 hours/day (and no practice on Sunday!) would bring a young magus with no warping whasoever to a Warping Score of 10+. That's clearly unrealistic.