What skill is hardest to master?

Hello everyone, what is your differet between beginning play crossfire and right now? Skill?
Some of us turn into pro players by master the skills and experience, but some are fail to master skills, and then they turn to other ways to be hackers to keep their high kdr or get fun on others. However, this topic will discuss what skill you feel hard to master, I will give you some skills that I feel it hard to master by myself:
- Sniper+ Quick Scope
- Sniper+ No Scope
- Sniper+ headshot
- Snipe through smoke
- Rifle + Tap (1-2 shots) + headshot + Long range
- Rifle + Burst (3-5 shots) + Headshot + Long range
- Rifle + Spray (over 5 shots) + Headshot + Long range/ Medium range
- Bhop on Staircase
- Bhop from high places to low places without damage to HP
- Hear and spot enemy where they exactly are
- Hear and spot enemy when they walk but make very low sound (change gun, drop from high high place to slow place, silencer gun)
- Hear ghost breath even they have breath noise down+ footstep noise down+ Bhop
- Control recoil when you are running or when your crosshair is expand
- Shot Gun + Headshot + Long range (20-30 meters)
- Checking corner successfully
- Prefire and headshot the enemies after you hear the sound even it is low
- Damage wallshot successfull + headshot + long range
- [Melee weapon] slash with knife kill enemies with Axe, shovel, kuruki or adv melee weapons.
- Master of m16 or m700 (headhost with them very easily)
- Use knife or melee weapon kill rifle, SMG, MG
- Gatling gun + Multiple kills or more
- Nade enemies + Multiple kills or more
- Spamshot + Headshot + Rifle
- Spamshot + multiple kills
- Jumpshot + headshot + sniper/ secondary weapon
- Teamwork without anyone in your team die
- 1 kill 8 in SND (no knife mode) or in ghost mode
These skill I mention above is without hack, if you use hack/ spy/ illegal program/ etc (suck things) then don't comment me you master that skill. Anyway just tell me your top 5 hardest skill to master or try to master in the list.