The event bonus is a global bonus that used to change with events. Now it is commonly referred to as the weekly bonus and changes every week at Sunday's Daily Reset to a combination of two from this list:
|Crystals from Mining||Always double|
|Pet Training||Always double|
A bonus being additive or multiplicative relates to how that bonus works with the other bonuses in the game. This means that by nature, multiplicative bonuses tend to be much more powerful than additive bonuses.
The wood bonus is additive with the Ascension Upgrade Log Gains.
The "Crystals from Mining" bonus only apply to the crystals you get from mining.