Here's the breakdown.
- Sentry Wards
- Long Term
- Bounty Hunter's Track
- Slardar's Amplify Damage
- Short Term / Conditional
- Zeus' Lightning Bolt & Ult
- Bloodseeker's Thirst
- Diffusal Blade
- Manta Style
- Counter-Intelligence (i.e. destroying Observer Wards)
- Blinding an enemy makes then very vulnerable to ganks
- Gives you more map control
- Observer Wards are on a cooldown, Sentries are not
- If they have an invisible hero and you're trying to push a tower, plop down a Sentry to make it safe for the next 2 minutes
- If you are defending a tower or your base, put one down to gain additional invisibility detection
- If you're afraid of being back doored, put one down at a vulnerable entrance to your base
- If the other team has a hero like Ursa (who regularly Smokes into Rosh), it's good to have a Sentry up on Rosh around the time Ursa hits level 7 (typical time Ursa will rosh)
- If the other team has a hero like Riki and you're all Roshing, put one down so there is no chance he will steal the Aegis
- They only last 2 minutes (versus Observer Wards which last 6)
- Ganking an Invis hero
- You need to know where they are so you can Dust
- Prevents them from using Invis to escape
- Team Fights
- Use it during a teamfight so the enemy invisible hero is revealed the entire time
- Counter-Ganking / Baiting
- In some cases, Dust can be used once an invis hero has initiated, then your team will ideally come to your aid and get an easy kill (NOTE: This is risky because some heroes can be 1-3 shot by a fed invis hero)
- Can be Purged
- Diffusal Blade (while offensively it slows and removes buffs), can be used defensively to get rid of debuffs on yourself/allies (i.e. things like Dust)
- Manta Style removes debuffs when used
- BKB gets rid of most debuffs
- Many heroes have spells that get rid of debuffs like Dust too
- Long Cooldown
- Does not Stack
- Preventing a gank from happening
- Gem is great for stopping a gank from happening
- A lot of invis heroes will sit on top of you until allies come to assist them
- Works the same way as a Sentry Ward, but it's mobile
- Get rid of all their vision
- Turning a Slight Advantage into a Huge One
- You've made one hero's spell useless (maybe more if they have multiple invis heroes or Shadow Blade users)
- True Sight works on illusions
- Gem is similar to an aura, and auras work on Illusions
- You and your illusions reveal (great for scouting out areas, split pushing, etc)
- Dropped on Death
- If you have invis heroes, this can now be used against you
- Costs 700g
- Long cooldown on the item in the shop
Long TermTrack and Amplify Damage work similarly to Dust. They DO NOT counter invisible heroes. You have to have vision of them before these spells work. They are great once you get the spell on them (though they can be purged).
If picking up Slardar or BH will ruin your lineup, DO NOT get them. There are items that replace their ults' functionality.
Short Term / ConditionalA lot of people forget heroes like Zeus and Bloodseeker can reveal invisible heroes. It's not necessarily a reason to pick either hero up, but it is something to keep in mind.
Zeus' Lightning Bolt reveals for 3 seconds after it has struck. Same goes for his Ult.
Countering DetectionThe big three are:
- Diffusal Blade
- You can activate it on yourself or allies for a positive effect of removing debuffs with no other side effects
- Manta Style
- Splitting into illusions will remove most negative debuffs like Dust
- Should remove most negative debuffs
Enemy team has Riki who has been initiating every team fight with a Smoke. The vision he grants his team allows for other heroes like Enigma to get very clean initiations.
Get a Gem. You will see Riki sneaking in and getting in position to use Smoke. Now you'll be able to kill him before he gets the chance
You're defending your Barracks (Rax) but your tower is down. Enemy team has a Bounty Hunter that is very fed. Your team is pretty much broke.
Buy Sentry Wards and place them around where your tower once stood. Sentry Wards don't give a lot of sight radius, but they give a huge amount of Invis Detection radius.
Because you're stationary (sitting there defending instead of moving around the map), this functions like a Gem. You can see Bounty Hunter sneaking up to pick off a support and jump him before he knows what happened.
You're trying to gank a free farming Clinkz. Your Mirana ults to give you all temporary invisibility to sneak up on Clinkz as he split pushes. Your team has only a bit of money.
Buy Dust. You know where he is and will be able to use the Dust so you can keep on him. If your team had more money, a Gem would work too, but it might not be worth the risk of losing it. Sentry Wards would not work here because Clinkz has a high move speed and would easily be able to move out of its detection range before you could do much.