Exp Stacking.

I've heard that Event + Card + Dual Blade Buff + Ring Mule works and is 14.4x but I heard that HS makes everything = 0.

I've heard that Ring mule does in fact work though, never tested it however.

Ring mule works because its counted outside of the total EXP as Ring Party Bonus EXP, so its exempt from the rule. Unless I heard wrong.

But yeah you can 8x with the Buff, 2x Card and 2x Event.