Introduction to Blight League
Blight League was introduced in Path of Exile 3.8, NPC Cassia was introduced into the game along with oils, anointments & blighted maps.Blight is essentially a tower defence, you have a pump on the map which you have to protect from waves of incoming monsters from different portals, these monsters can only walk along the tendrils connecting to the pump and you can also choose to build towers with different effects to help protect the pump.
Blight Tower’s
In total there are six different tower types with initial effects that can be upgraded to an even greater effect at maximum level. Towers are not always necessary as you get closer to end-game content, the chances are you will be able to deal with the monsters with your abilities alone, however, towards the start of the league these towers are extremely useful to help you clear the waves of monsters.At the bottom of your screen when engaging in a blight encounter there will be several portals indicating the number of tendrils you will have to clear, some of these portals will have images of tower types on them, this means that the monsters spawning from those portals will be more resistant to those tower types.

Upgraded Tower Types
Below is a cheat sheet showing what each upgraded tower type in blight does:

Oils & Anointments
Blight introduced oils and anointing in 3.8, there are a total of 12 oils that were introduced, the rarest being Golden Oil. Oils only use are for anointing items, when you speak to Cassia she gives you the option to anoint an item with a powerful enchantment which varies depending on what item you use it on, anointments are exclusive to Amulets, Rings, Blighted Maps and specific Blight uniques.Anointments are predominantly used on Amulets, this is because you can anoint an amulet with a notable passive skill from the skill tree, to anoint an item you need 3 specific oils with whatever colour the passive requires, you can see the
full list of amulet anointments here. Some specific Blight uniques can also be anointed with a notable passive.
Blighted Maps
Blighted maps are a fun, massive tower defence on a whole map that always spawns 20 portals. For five minutes you’ll have to protect the pump and fend off against hordes of monsters and bosses, blight maps are a great option for party play as more people can cover different parts of the Blight.Blighted maps can be anointed to increase the difficulty, increase experience gain or potentially get greater rewards, see the full list
here.

How to complete Blighted Maps
Blighted maps can be tricky, especially if you’re doing them alone – one of the tried and tested ways players manage to complete them is to spam “Scout” minion towers. Scout minions are little flying drones with long-range attacks that tear through monsters, they will clear most trash mobs leaving you to focus on the remaining survivors and focus more clearly on the bosses.
Anointing and Rolling Blighted Maps
A few players have tested out different methods of rolling Blighted maps, upgrading the rarity of a map and giving it additional modifiers does not affect the chest loot rewards, only the loot explosion at the end, to make it a lot easier you should always do Blighted maps on normal rarity with 20% quality.The most profitable, cost effect oil that was tested was
Teal oil, however since most oils aren’t extremely rare anymore, you can probably use
Crimson which gives even more lucky chests at the end of the map.