Just wondering what effects/technologies were used to make the dota2 playing field. How did they combine the different paths together? (dirt ground to grass, water to steps) How were the rocks around the radiant's base created? What about the fire? (Is it just a bunch of particles or something else with a shader effect?) Thanks.

Here's what the terrain looks like

http://images1.pcgamesn.com//Phantom%20Assassin%20Imp%201.jpg

A quick google search reveals that it is being developed using the Source engine. If you look up source engine features like this, you should get an idea of what the engine can support. Under "Materials" it states "Versatile Multi-Texture Blending. Define blend masks with variable sharp edges, combine textures using multiple different modes, and apply per-surface color correction."

Some google searching reveals a link talking about something that looks similar: Multitexturing in DX11 . Here is an XNA link from Riemers. Here is a neat link about Multitexture from the Polycount Wiki.

As for the per-surface color correction, the best I could find was something from GPU Gems- Chapter 24Using Lookup Tables to Accelerate Color Transformations.UDN uses it as a link when talking about Color Grading.

It is then possible and likely that the maps were created in the Valve Hammer editor.

Although usually it is common practice to create a lot of levels or the components for levels for 3d games inside of 3d modeling applications.