Zugspitz Ultratrail race impact in Mittenwald?

You can use the even less expensive Werdenfels Ticket to go to Mittenwald and you are not restricted on time during week days, 20 EUR plus 6 EUR each additional passenger up to 5 traveling together. ie take the 7:32 train.

Sam how do I find this Werdenfels ticket? When I do point to point tickets on DB site that option doesn't come up. I've seen others reference this ticket as well. We are a family of 4 (2 adults & 2 children 14 and 11). I've tried the website both in English and in German and neither time did a point to point search bring this option up, only Bayern or flexi. I'm intrigued to learn more!

I've just tested it: requesting 19 Jun, dep. Munich 7:32, two adults (children up to 14 travel free), brings up as cheapest offer the Werdenfels ticket (€26).

BTW, I don't think that your trip to Mittenwald is affected by that Zugspitz event.

Yes, when I look, if I enter 2 adults and 2 children, I only get option for Bayern Ticket, with no early departure allowed. Solution, consider them adults, then for 4 adults gives a Werdenfels ticket for 38 EUR and you can leave early. Apparently kids don't ride free with the Werdenfels Ticket. I don't think there is anything wrong with that, as long as you include them as adults on the Ticket. When you buy it out of a ticket machine, write the names of all travelers on the back of the ticket.

Edit: The actual DB website page (German only, use google translate) does say that kids ride free with the Werdenfels ticket. Websites sometimes are not always perfect. Apparently, when the journey planner sees kids, it defaults to Bayern Ticket, then will not show it as eligible before 9 am. When you buy the tickets, you might want to confirm this with a DB agent, even if you have to pay the 2 EUR window fee. 28 EUR is still less than 38 EUR.
https://www.bahn.de/p/view/angebot/regio/regionale-tickets/bayern/regio-ticket-werdenfels.shtml

The conditions for the werdenfels ticket state very clearly:

"3.1.1 Ein „Regio-Ticket Werdenfels“ kann genutzt werden von bis zu fünf gemeinsam rei-
senden Personen.
3.1.2 Darüber hinaus können bis zu 3 Kindern im Alter zwischen 6 Jahren bis einschließlich
14 Jahren unentgeltlich mitgenommen werden.
3.1.3 Kinder nach Nr. 3.1.2 sowie Kinder bis einschließlich 5 Jahren werden ohne Fahrkarte
unentgeltlich befördert. Bei der Ermittlung der Personenzahl werden sie nicht gezählt."

So they can simply book a werdenfels ticket for two adults (€26). The children simply don't count and need not to be indicated when booking.

The Zugspitz Ultratrail Is anyone familiar with this race and the impact on the town of Mittenwald? I don't know about Mittenwald, but I know about Garmisch-Partenkirchen.... I didn't even realize the race was going on until the runners starting passing me on the same hiking trails I was taking to Königshaus am Schachen. Judging from what I saw, it isn't a particularly big event.

Thanks everyone for the very useful information. I'm glad to hear the race would probably have little impact (thx Tom & sla019) and I'm happy to have learnt all about the Werdenfels ticket. As a follow up I had emailed the DB who like sla019 & Sam concurred that since children ride free I don't have to include them in the ticket sale.