Here's a list of count thresholds to hit by certain checkpoints for various keystones. This is intended to be a basic cheatsheet when just winging the path on lower keys using common routes. Unfortunately this season changes counts between keystones 1-9 and 10+, as the level 10 affix mobs provide count, making a simple cheat sheet a little less useful than past seasons. Additionally, this season most dungeons are ones that are harder to end up under count on; being over count is a much bigger problem in several of the current keys. With that in mind, I try to provide some tips on mobs that you can "walk by" skip rather than focusing on percentages to hit.
• So'leah's Gambit
Keylevel 1-9: 37.9% in the murloc area (hug left coast and only pull what you need to)
Keylevel 10+: At least 35.3% in the murloc area, but must pull every mob after this point to hit 100%
• Streets of Wonder
n/a - just make sure you're at 100% before you go up to last boss, as he has no trash.
• Mechagon Junkyard
n/a - the challenge will be not going over count. Pull only what you need to to safely do bosses and navigate around, and you should be okay. If you're under, there is plenty to pull on the way to the last boss.
• Mechagon Workshop
Keylevel 1-9: 65.6% after third boss
Keylevel 10+: 65% after third boss.
However, if you're not doing any skips, you will be over count by the end so you may not need to worry about this.
• Iron Docks
Keystone 1-9: 57.5% minimum at second boss.
Keystone 10+: 58.7% at second boss, assuming you pull both the sidepacks on the way to the third boss. If you're at 72% or higher, you can skip the sidepacks.
Clear ample space around your path on the way to the first boss and at him, and then try to hit as much as you can with the big wheels, and you should be good.
• Grimrail Depot
n/a - On rails, just pull everything you need to pull to progress and you'll hit (slight over) 100%. If you're doing a 10+ you can skip the two Overseers on the right on the way to the first boss. You will need their percent in 2-9 keys range, however.
• Lower Karazhan
n/a - It's going to be very hard to be under count here without doing the death skip, but if you do that, there is ample trash to choose from to make up count around every boss.
• Upper Karazhan
n/a - You will go way over count just pulling everything on your path. You can safely skip one Damaged Golem at the top of the stairs before Curator, all the fel bats, the out of the way rats and spiders in the Mana Devourer's room and you will still be over count.
Also, here is a great weakaura that prints some of this data https://wago.io/_PCyfyfoR in chat during your run. This is NOT MY WEAKAURA. I'm just listing because people might find it useful and it serves a similar function to this cheatsheet. I use it and highly recommend it, winging keys or otherwise.
Depreciated Keys: