World of Warcraft 's mythic+ system allows for each dungeon to feel completely different with each passing week. Here is each affix with a difficulty attached to each, along with some of the ways to deal with them.

Baseline Affixes (You will always have one of these)

Tyrannical

Buffing bosses health by 40% and increasing their damage by up to 15%. This makes bosses much tougher, forcing you to be more precise at their mechanics. Many mechanics will one shot on higher keys. The increased health will force you to deal with the mechanics for longer as well.

Fortified

Buffing non-boss enemy's health by 20% and increasing their damage by up to 30%. This can make certain pulls very difficult. CCing enemies on tough pulls will almost be required. Make sure you are interrupting enemies and CCing them whenever possible.

Level 4 Affixes (These are applied on any key +4 or higher)

Raging (Easy)

When enemies reach 30% health they enrage, increasing the damage their deal by 100%. This can make certain enemies very deadly. Stunning them when they reach 30% can allow you to kill them without taking any additional damage. Druids and certain hunter pets can also sooth enrage, removing the damage increase. 

Sanguine (Easy)

When enemies die they create a pool of blood where they died, healing other enemies and damaging players in the area. This requires your tank to kite the enemies out of the blood once they start to die. Can be helpful to have a class that can move enemies such as a DK's Death Grip or Druid's Typhoon to push casters out of blood. Line of sight and moving out of range can also force enemies to move out of the blood.

Bursting (Medium)

When a non-boss enemy died it explodes, applying a debuff to all players that deals 5% of their max health per second for four seconds. This effect can stack indefinitely. Be careful killing multiple enemies at the same time. 

Bolstering (Medium)

When enemies die they buff other nearby enemies, increasing their health and damage by 20%, stacking indefinitely. Try to kill enemies all at the same time. Enemies out of combat or 40 yards away will not receive the buff. Enemies affected by DH Imprison will also not receive the buff but other forms of CC will, as long as they put the target in combat.

Teeming (Hard)

More non-boss enemies spawn and the required number of forces in increased. This affix will require you to CC and interrupt more enemies. Can be especially deadly on Fortified weeks.

Level 7 Affixes (These are applied on any key +7 or higher)

Volcanic (Easy)

Periodically when in combat, flame geysers will spawn beneath players at range. This can spawn on melee if they are far enough from the enemy. The geysers are easy to avoid and do not always spawn right under you, allowing you to stand still and not be hit.

Quaking (Easy)

Periodically, players will deal 20% of their max health to themselves and all allies near them as well as interrupting spell casts. You have about 2 seconds of warning to spread out and the damage is not usually deadly. 

Skittish (Easy)

Tanks generate 75% less threat, meaning DPS are going to need to watch their aggro. Slowing DPS or focusing the tanks target will allow you to stay safe and avoid aggroing mobs to come attack you. Hunter's and Rogue's Misdirect and Tricks of the Trade can make these weeks much easier as the extra threat also allows other DPS to go ham.

Necrotic (Medium)

Enemy melee attacks apply a debuff that deals damage and reduces healing received by 3% stacking indefinitely. These stacks last 9 seconds and are dispelled when you leave combat. Tanks should kite enemies until the debuff wears off. Blood DK tanks are strong these weeks due to their Anti-Magic Shell, which makes them immune to receiving the debuff for 5 seconds. This allows you to only have to avoid melee attacks for 4 seconds to allow AMS to negate the rest.

Explosive (Medium)

Enemies have a chance to spawn explosive orbs, which detonate after 5 seconds, dealing 50% of all players max health in damage. These have very little health but cannot be AoE'd. Players should target and kill these whenever possible. Can be very difficult on teeming weeks or on large packs of enemies. Explosives can be LoS'd and only damage players within 40 yards of their explosion.

Grievous (Hard)

When players are below 90% health they acquire a debuff until they are healed above 90% health. This debuff deals 2% of the players max hp per 3 seconds. Every other time you take damage you gain another stack, up to 5 stacks. This can be deadly if not managed correctly. DPS should save heals for when they can heal themselves above 90% and clear the debuff. All enemies abilities can be deadly, even a mere 11% of someone's health can create much more healing required. Healers should try to keep everyone topped off as much as possible and focus on removing grievous from one person at a time.

Level 10 Affix (This is applied to every M+ level 10 or higher)

Infested (Medium)

Certain enemies will be infested, healing other nearby enemies within 8 yards for 5% of their max health per second. When the infested enemy died, it spawns two Spawns of G'huun which seek out other enemies, upon reaching them, they cast Infest, a 1 second cast which if successful, infests the enemy, repeating the cycle. These infested enemies should be CC'd and killed after the rest of a pack or killed first. Spawns of G'huun can be CC'd, giving you more time to kill them. These infested mobs are random each week but stay on the same enemies per dungeon on the certain week. Another thing to note is that if no enemies are within 40 yards when a Spawn of G'huun is created, it will start to attack the nearest player. 

You can check out my dungeon tier list and how to deal with them here.