Contact the author of this modpack with the crash report.
If you're putting this together yourself, remove / update mods and try to find a working combination.
The fewer coremods the better your chances of success.
I see coremods. I don't think this is supported, but I don't see it in the EAQ.
Loaded coremods (and transformers):
FairyLightsLoadingPlugin (fairylights-1.2-1.8.jar)
com.pau101.fairylights.core.FairyLightsClassTransformer
GenderLoadingPlugin ([1.8]Gender-1.0.5.jar)
net.iPixeli.Gender.coremod.GenderClassTransformer
In case anyone finds this thread but not the comment by kenzierocks, the OSX vecmath issue is fixed in ForgeGradle 2.0-SNAPSHOT (at this time 2.0.3 not yet released)
(this is the top Google link for the cause stacktrace, THANK YOU for posting a stacktrace so that others can find a solution!)
OptiFine 1.8.8 HD U F5 is not compatible with any version of MinecraftForge 1.8.8 (at this time, forge-11.14.4.1590 does not work with the same stacktrace)
See this wiki page with more information. (please update the wiki if there is a known working version)
http://www.minecraftforge.net/wiki/OptiFine_Compatibility_Guide
Customer support should not be so ego driven.
Post working versions and don't waste your time assigning blame. It's fine if you personally dislike OF for some reason, but it's still recommended in this forum's FAQ.
This is a well written report. Possibly improved by a copy-paste of the stack trace so that Google will lead more people to the right solution.
There are some terrible mixed messages from the forge contributors about OptiFine support. The latest 1.8 works with OptiFine. I'll update when I can test and give exact versions.
This is a support recommendation not a criticism of anyone's engineering. It is also not worth arguing about, but you're going to get people Googling and finding this post which has multiple solutions (uninstall OptiFine, downgrade Forge)
I recommend the following as a sticky:
EDIT: I also recommend clarifying OptiFine in the rules sticky, since it appears to be supported according to that content.
If Microsoft is smart they will be optimizing mc/win10 to run on azure and pricing people into cheaper realms. This will crush the existing market, but only if they can capture the modding scene.
To do that they'll need to pursue a forge or bukkit style API. This could also get people using C# which would be a strategic win.