Alchemy Style trailer. From this, we see it has its own gauge and it's own item slot when out on a hunt, similar to the wystones from MH4U. You fill the gauge by attacking, and the higher the guage, the more you can shake the barrel, which presumably increases its effects. You combine items you already own to make things you can use to buff yourself and your allies, or attack with. "Alchemy" is a surprisingly perfect name for it.
A trailer for a new mechanic, Style Power. It seems to be a buff that you can equip to any of your hunter arts, and it activates whenever you use an art. I'm not entirely certain from watching this trailer about what its effects are exactly. Maybe I'll look into it when it's... not the middle of the night.