How do I tell what elemental vulnerabilities are on Blight mobs?

The screen right now is so cluttered and confusing I have zero idea how to tell what towers to place in order to make the tower defense a lot easier.

Where, and how do I exactly figure out what elemental weaknesses the mobs will have? What elements correspond with what weakness?

Solution 1:

There are no type advantages against blight monsters, they only have resistances. This means every tower is equally effective against all monsters unless it has resistance to a specific tower type. The symbol is telling you what type of monsters are spawning from that location. You can see it above the portal itself, on the minimap and on the UI towards the bottom of the screen.

For example, if it shows a snowflake signaling cold monsters, those monsters cannot be chilled/frozen by any source, and take heavily reduced damage from cold towers. Another example previously given is that all physical based monsters, signaled by the fist, are immune to stuns and knockback from all sources.

The only exception to this is flying monsters, but there doesn't seem to be any indicator that they are spawning, so keep an eye out for them. They will not be affected by the ground based physical tower, and will fly over minions from your towers and other blight monsters.