Honestly, the OMG things from box 1 and 2 seem to be more unique than "OMG." And nothing basic like snail mucin or synake or plant placenta or pig collagen shock me in any way. I love the OMG boxes because they do contain some great products, and the value is definitely there for me.
Horse oil isn't exactly a popular thing, and Pure Smile is a Japanese brand. I've only seen two Korean items with it, and both stated Horse Oil clearly in the title. It's not a big thing, and I would not expect it in any of the Memeboxes. I don't think Memebox would even feature the Mayu sheet masks in the boxes, I really think it just happened to be one of the several varieties, I don't think they selected that purposely. The skincare products I've seen with horse oil were from well established brands and were on the expensive side, I really do not believe that those sorts of brands are going to try to break into the US market with such a product.
The OMG #3 was the box that they said was going to really shock and amaze us. But the spoiler was a donkey milk oil mist. If that's what they think will shock and intrigue us, I think OMG 4 won't be much different. I mean, this is what, the 4th donkey milk product?