Until the land starts to be cleared of Blight, most of the mobs you will fight will be tainted variants.
Non-Blightfall specific information about these creatures can be found at Thaumcraft 4's Taint Page.
Tainted Vanilla CreaturesEdit
The biggest disadvantage of these creatures is that they only drop tainted goo or taint tendrils, making the collection of feathers, leather, wool and meat a serious challenge until you can get their untainted counterpart to spawn in your biodome. You will also notice that these creatures get a 'potion effect' on fibrous taint - this is actually a healing effect for them. Tainted livestock will attack their untainted variety, so it is vital that you do not let taint anywhere near your livestock pens. This doesn't seem to be the case for tainted villagers. Most of these creatures can be returned to their untainted version using a Purity Focus from the BlightBuster mod, which can be researched using Thaumcraft research mechanics.
An untainted mob will take periodic damage when walking on tainted land, and often will die on it. When this happens, they have a chance to become a tainted version of themselves or a Thaumic Slime.
Tainted Chickens - These things are FAST and have hit-and-run tactics. It is suggested to kill these on sight versus trying to run past them. Occasionally hitting them will cause them to run off - use this to your advantage
Tainted Cows - These things are incredibly durable, as they have about 10 hearts. These are relatively rare and you'll often find leather/meat from the original creature nearby.
Tainted Sheep - These are quite common and have the added ability of being able to spread fibrous taint when performing their 'eating grass' animation.
Tainted Pigs - These are also quite common and seem to have a dash-attack.
Tainted Villagers - These still seem to have the habit of hiding in their houses during the day, which can be problematic when exploring/raiding/cleaning villages. However, the real threat in villages and when exploring are Tainted Custom NPCs.
Thaumic Slimes - Similar to the slimes, these are more aggressive and can make off-shoots which can slip past biodome glass if they get the angle right. Mobs that do not have a tainted form (e.g. slimes, Tinker slimes, bats, Endermen) will become these if they die on tainted ground.
Tainted Creepers - Thanks to the default settings in Blightfall, there is no land damage associated with their explosion, but it immediately taints the land within the surrounding blast radius.
This category specifically spawns in tainted land covered by fibrous taint (Taintacles and Tainted Spores) or crusted taint (Swarm Spawner). Most of these are appear on the minimap as question marks.
Taintacles - These creatures grow out of the ground. While their base is fixed in place, they continually lash out at creatures around them. They can attack out-of-reach opponents by spawning several small Taintacles in their vicinity. They cannot do this in water, or outside of fibrous taint - they will also take damage and eventually die if the land they are on is no longer tainted. It is recommended to steer as far off from these as possible, despite how common they are.
Swarm Spawners - These appear as a block of crusted taint swirling with a Taint Swarm. They produce Taint Swarms when a player is still a considerable distance away. Despite their blocklike appearance, they are in fact mobs; when struck, they will flash red and take damage, They have 35 hearts of health. Upon destroying one, it will spawn two additional Taint Swarms.
Taint Swarms - These glowing swarms of purple lights attack all passing players, and can fly up to attack those who thought they were safely out of reach. Despite the swarm's immaterial appearance, it can be attacked with a weapon in the usual fashion. They have at least 10 hearts of health, and possibly up to twice that. The Sword of the Zephyr is a possible solution to these creatures.
Tainted Spores - These fleshy-appearing blocks will shower purplish particles when approached, then once a player comes within 3-4 blocks, bursts into a group of Tainted Crawlers. They will likewise burst if attacked or the land they are on is no longer tainted.
Tainted Crawlers - Tiny purple spiders with the typical tainted look. They have 2.5 hearts of health and deal 1 heart of damage when they attack. Due to their source, they typically come in groups of 3-5. They are unaware they can easily take fall damage, which can be used to the player's advantage.
Tainted Custom NPCsEdit
There are a number of tainted NPCs in Blightfall - these are completely unaffected by the purity focus and are often incredibly deadly to the player. They will often appear at key locations on the map such as quest locations and particularly villages. If you are paying attention to your radar, you can spot them and be prepared, as many of these have ranged attacks.
This list is incomplete - if you find tactics or weapons that are reliably effective against these creatures, please add it in the comments or the appropriate section.
Tainted Botanist - These guys are equipped with Mana Blasters and Mana Tablet and seem to have an incredible healing rate. One can be found at the Iceberg Scout Location, another is found at the Purple Mystical Flower Location. Will kill in one or two shots in most circumstances.
Tainted Thaumaturge - Can be found in the Iceberg Tunnels, other locations are uncertain. Attack patterns are entertaining enough to not post on this wiki and will obliterate anyone who is not packed in high-tier armour.
Tainted Archer/Sniper - Able to kill an unarmoured player in a single shot. Present in villages, often in towers or churchlike structures, also present in forests and jungles. Will persist and have a very large radius.
Tainted Warrior - Will eat your entire ass, but not as much as the Tainted Hero will.
Tainted Scout - ?
Tainted King - Nowhere near as powerful as anything else on this list. He won't last three hits, but he drops the ingredients for a Silverwood Wand plus a CustomNPCs crown. Only one in the world.
Tainted Hematurge - Notably found in the Obsidian Tower, he is equipped with Bound Armor and a Bound Sword from Blood Magic. Caution is recommended when fighting him, as he is capable of killing an unarmored foe in one shot. He is also very slow, however, and does not have any ranged attacks.
Tainted Hero - Even with full armour and a full-power Signalum Crossbow, your chances of defeating this are incredibly low. It's best to catch them with a Safari Net instead of engaging them, then dealing with them as you see fit later on.
A good strategy is to avoid attacking any tainted NPCs when in melee range, as most of these have either powerful ranged attacks, powerful melee attacks (Like the hematurge), or even both. Recommended to fight these at range, especially if you can hit them outside of their aggro range so they won't be able to retaliate.