There's a lot going on in that image.
On-screen:
First, he's chucking bottles of Holy Water. You can see the splashes / shards and it appears to be turning the material it hits into a different material type. Since there's Ebonstone around, I'm thinking maybe the Holy Water is used to 'purify' Demonite into, say "Angel-ite", which explains the 'Holy look' of the new sword and hammer. They look like angelic weapons.
Not sure what's up with the Holy Water itself; it doesn't appear to be in the inventory, but one is clearly being thrown. There's a larger bottle of the Holy Water with "165" over it, so perhaps they are changing the method for using missile weapons; you pick them up and can 'throw' them at any time.
Nevermind: "You can now directly use items that are being held with your mouse (instead of always dropping it.) This also enables you to place items without putting them on your hotbar first. "
Guess that will make placing Torches easier too.
Second, the armor is red; something we haven't seen before, alluding to yet another new material type. It's also used on three inventory items (Polearm, drill, 'chainsaw').
Is that a new background too? It looks like the rocky layer, but corrupted.
Player sprite has some degree of flicker on him, not sure what that's from, could be anything.
Inventory:
Obvious new Sword, Polearm, Hammer, Mace (looks like the Morning Star, could this be their "Castlevania"-themed pack? I was hoping for Metroid first =p).
Odd placement of the Orb of Light, right there in the second slot. Maybe it won't suck anymore?
We've known about Drills before, this is just a new look.
The "Chainsaw" in the 5th slot looks more like a rifle barrel to me, plus he's carrying bullets but no other gun. He's carrying arrows too, but now Bow, so I could be wrong.
The Bottle in the 9th slot doesn't match the holy water he's throwing, so I have no idea what that could be. Maybe it's a new potion type or 'Evil Water' used to corrupt? No clue.
He also appears to be carrying 220 of some soft blue dirt I don't remember seeing before.
Equipment:
New Boots, perhaps an upgraded version of the Hermes boots. The blue color makes me think 'water-walking', but that's just a random guess. For all we know, they could just have liked the color blue.
Looks like some kind of inverted teardrop or crystal, not sure what's up with that. Some people have suggested it's a "Cloud in a Balloon", a combination of Shiny Red Balloon and Cloud in a Bottle.
Could be a new icon for the Depth Meter, or some kind of other meter... Perhaps a Geiger Counter for detecting radioactive material deposits? Maybe that's what he's using the Holy Water to purify; some kind of highly dangerous material.
Not sure what's up with the snorkel-looking thing. It may be it's just that; a new accessory-version of the Diving Mask.
New Shield too, no idea what it could be for. Symbol doesn't ring a bell either.
