The special seasonal event modes Valve create for Dota 2 [official site] are slightly less novel now that all and sundry can make their own modes, but Valve's are always jolly fancy. If you fancy a good Spooky Week spooking, venture into their the Haunted Colosseum. Diretide begone! Haunted Colosseum is a 5v5 point capture mode in a new map with deadly traps and nasty pumpkinmonsters, and it's out now.
Entering the Haunted Colosseum, teams will fight over control points which grant a steady flow of points. The more they control, the faster the points come in, and the first to 5,000 wins. A little comeback aid comes when your enemy scores 1,000 points, spawning honking great Behemoths that'll help you by stomping around murdering people. Making all the capturing and chasing more complicated are traps players can trigger, like giant murderpendulums scything across control points, and mouths in walls spewing poison or fire. Some are triggered by switches and some simply by touch, so good luck with that.
You can download Haunted Colosseum from the Steam Workshop and play it through the Custom Games section. Pop-ups will helpfully remind you of all this the first time you launch Dota 2 after updating anyway. Yesterday also brought a patch making the Custom Games section friendlier, changing Low Priority queue games from All Random mode to Single Draft (god, what hell that must have been - I'm glad I never experienced it), and more.
Here's Valve's vid showing the highlights of a round:
Or for a full round, here are those DotaCinema folks playing. I've only watched a bit, but I imagine they say some naughty words so beware if you're in polite company: