The bat is a man of mystery, insanity, and danger. He was taken into the woods by his not slave that he now rides and uses to his advantage. His mighty lasso can initiate the craziest teamfights and his firey flying skills highlight his mobility.
Makes all of his abilities stringer, upgrade this if you're going offlane lane dominant. max it second though, because it can be used to help out your lane presence and depush, but it only synergizes if you have Firefly maxed, which we'll talk about here in a second.
Knockback and AOE damage, not super useful, but if you want to become a better bat player it can help with your ganks by changing your enemy's position. The DPS afterwards with sticky napalm helps all the more.
The most important skill for the bat. It's his escape, his wave clear and his primary damaging ability. Use this while using Flaming Lasso to damage the guy you're dragging or use it to survive the laning stage and become dominant. Ideally, this skill in combination with Sticky Napalm should win you the lane.
This is your big initiation ability, or counter-initiation, depending on how the teamfight is going and when you get there. This ability does no damage until you get Aggs, so use it to drag in kills before you get aggs, when you can change into a bit more of a pickoff choice, picking off pesky Snipers, Bloodseekers, Slarks, Drows, any low health hero is yours for the whipping.
Blink dagger, is core on batrider, it allows you to initiate from farther range and without having to run up to your target, this makes your initiation less predictable.
Aggs, can be bought second or third depending on your need for it, are your other lanes getting kills without your help? Probably later is OK. If not, buy it ASAP after blink dagger.
Arcane Boots, helps with your mana issues, early game use it to regain some mana for bettering your ganks. Purchase it second or third based on when you want to buy Aggs.
Force staff, used to GTFO once you've lassoed someone (or several people) and bring them to the crushing jaws of your team. Also good for HP regen and mana regen from the intelligence you get.
Late Game Itemization
Almost always, I disassemble arcanes for Aether Lens. It helps with mana regen, allows you to hit people with your lasso and Napalm from farther away, and gets you better mana pool to start with. I tend not to do this if I'm going jungle, as the bonus farm you get allows you to become more of a carry than a support, Late game though, when you become more of a support feel free to go Lens.
BKB is great, not just for you, but for your team. It lets you initiate free of charge and brings you into the forefront of fights. Using this item would almost be core, if it weren't for right click focused teams. If you have a damage dealer on the enemy team like an AM or a PL, this isn't necessary unless you have something like an Invoker or Tinker to fight against, just someone that spams spells. In this case, you should also get wand.
A lot of the other item choices are situational, use these if you get the basic concept of bat, and are playing him well, but can't seem to do your job or aren't as effective in battle. If you want to see further descriptions, feel free to leave a comment.
Level 1 (opening phase)
The opening phase of the game, buy you some tangoes and get ready to get harassed because you are very easy to push out of lane before level 4. The opening phase is just to get levels, gold isn't necessary. (you can probably get a wand at this stage, should only take a few last hits) Denying is your friend, don't buy quelling unless you're having serious problems.
Level 4 (clearing phase)
This is when your Depush gets nutty if you are doing the traditional build, level 2 Firefly and Napalm should be enough to clear pretty much anything that comes at you, if you're laning with a core, like a Necro or Shaker, use this combo to zone and clear, not to push. YOu can also clear jungle camps with this, just pull both camps and clear them with Napalm and Firefly. This makes you vulnerable if you do this in the direction of the shrine, so pull towards the mid lane when you would normally stack to get the bonus gold and experience, you can even stack ancients on your way back if you have a sven or AM to clear them.
Level 6 (ganking phase
About here, find somewhere to gank. anywhere, just gank a lane. Pretty much as soon as you hit 6, let your team know, then they can rip 'em down from the sky from low health. Your goal is to have the most assists by 15 mins. If you can get a couple of kills by level 8, and you didn't put a point into Flamebreak already, go ahead and do so. Smoke ganking with another support or offlaner helps because it gets you more kill potential if they have the nukes to take him down.
Whenever you get Aggs (Solo Pickoff phase)
Whenever you get Aggs, you can start solo killing supports and weak heroes with low mobility. This is a great use of your ult because it guarantees a kill. but remember to get the 15% cooldown talent so you have this up for fights, also tell your team when your ult is down.
When you run out of slots (team fight phase)
Stay with your team and initiate when you feel like a teamfight is going to start.
When he Sux
Duel locks you down hard, your health can't sustain it if they have a good support for duels.
Press the attack dispels Flaming Lasso
Aphotic shield and Borrowed time dispel Flaming Lasso
DO NOT PICK BAT AGAINST ORACLE. PERIOD
Don't drag him into an easy ravage
invis heroes, can't lasso 'em if you can't see 'em.
semi counter, if she uses exorcism beforehand, it can right **** your team just like a ravage.
When He Ain't
Locking down a single meepo with Lasso can kill 'em right quick.
Treant Protector/Monkey King
Tree reliant, firefly removes trees.
Slowing him down and not letting him cast spells helps.
lockdown against a weak right-click carry.
only use this if your offlaner demands solo farm, then you become a roamer, working off your ult and Firefly to counter heroes like Treant and MK offlane.
Start with Iron talon or Quelling Tango Salve if you feel like you need more Regen.
Get Midas ASAP
Try to win