Answered A complete list of additive vs multiplicative EXP modifiers

generally* speaking these types are multiplied:

• Cash tab coupon OR etc tab coupon
• Use tab buffs for 1.5x or 2x or 3x
• 2x event
• Ring of torment

There's also a few class specific skills that are multiplied bonuses such as showdown.

*note that 3x exp cash coupon will not stack in any way with 2x event. Do not use them together.

If you use "normal" buffs meaning 2x in each of the 3 categories above you'll have 8x exp (9.2x exp while ring or torment is active).

All other effects are additive:

• HS (or BT exp buff, but it's only 30%)
  
• Rune buff (use evan link to extend duration)
• Mercedes link skill
• Zero legion effect
• Legion exp grid region
• Eluna exp skill (granted by eluna equip)
  
• Item exp buffs such as pendant of spirit
  
• Potion type 1: alchemy
• Potion type 2: monster park gold
• Kinship ring
• Burning stages on your map
• MVP exp buff - the cash shop tab weather effect
• Aran link increases the exp of combo orbs
• Class specific exp increase (lucky dice - 6, etc)
• Event specific exp increases are generally additive
  

There could be more I have missed. Also there are occasionally events that boost exp such as chocco buff which would also be additive.

 

We can add ring of torment to the list now. It's a 1.15x multiplied buff for 15 minutes, 30 minute cd.