--Firefly is taken at level 1 because you don't know what will happen in the first few minutes and you can use this as a escape tool - walk through trees (or cliffs, if there are any nearby) and try to reach the tower asap. You will use this skill mainly to apply damage, as it works awesome, combined with Sticky Napalm

--It doesn't matter which skill you will learn at level 2 and 3. If you want to go for a first blood - learn Sticky Napalm, otherwise - learn Flamebreak.

--Sticky Napalm is always maxed first. This is the skill that makes Batrider that powerful. There are 3 awesome things about this spell. 1 - it deals bonus damage each time you deal damage to affected unit - 10/15/20/25*Stacks (up to 10 stacks). 2 - It slows by 9% per stack, which is uberimba and you will use this as a huge huge advantage. 3 - It slows turnrate by 70% - that means that it will take 70% more time for your enemy to turn and to start running. Note that 10 stacks are 250 bonus damage each time you damage an affected unit! Each damage counts, except the burning damage from Radiance.

--Flamebreak This skill is your nuke. It deals decent damage and knockbacks hit units. You will use this mainly to clear creepwaves (combined with ~3-4 stacks from Sticky Napalm) and to kill fleeing heroes. It affects units within 400 AoE of the main unit that was hit by the flamebreak, so don't worry - you don't have to be that accurate, just make sure you will hit something.

--Flaming Lasso This is your awesome disable. It disables the trapped unit and drags him with you for 4 seconds. REMEMBER, use this only when you have stacked Sticky Napalm at least 3-4 times and when you have activated Firefly, because it is it's main purpose. Of course, you can use this skill first, but make sure that you are surrounded by high damage dealers, so your damage from your skill isn't that much needed. The Flaming Lasso will break, if the distance between you and the dragged unit is more than 400 units, so never blink while you drag someone.

--The good thing about Batrider is that he doesn't need much items to show his full potential. Rush Urn of Shadows - the str bonus is good and you won't be paper hero, also sobi mask gives you nice mana regen, which will help you spamming Sticky Napalm. Urn will be good if you get this very early, since you have the potential to make lots of kills in the early game. And the most important - URN OF SHADOWS DEALS 25 DAMAGE PER SECOND, WHICH MEANS 25 + 25*STACKS IN DPS. (urn's dps won't do bonus damage to napalmed units, excuse me for this mistake) This, combined with Firefly can literally fry an enemy hero. So i think that Urn is a must. Buy Magic Wand if you face casters, but it's just an optional, although it provides good bonuses as well. Buy Power Treads (Int) lately, as it provides good enough MS bonus(remember that you have awesome slow and a disable, so you don't need huge ms boost) and buy perservance then, as it provides very good regen. With this build you got +11 strenght (+209 HP), +5 Agility, +15 Mana and overall +25 damage. You don't need attack damage that much, your skills will do the job instead.

--Why Force Staff rather than Dagger? Force Staff is awesome for Batrider. It gives you 10 Damage, 10 Intelligence and 10 Attack Speed (20 Damage and 130 Mana) and the ability to 'force' unit which pushes a unit 600 units in the direction it is facing. If you choose Dagger you will use it mainly to initiate, but if you use it while you are dragging someone, the lasso will break. For the same gold (well, 100 gold more actually) you get a item that provides awesome stats. You can either initiate with force staff (if the enemy is facing you - use force staff at him and then use your ulti, or target yourself with force to get close enough to cast your ulti) or use it while dragging, as it won't break the lasso. This is why I prefer Force Staff rather than Blink Dagger.

--Linken's Sphere. I suggest to buy Linkens right after you make Force Staff, because you already have perseverance. As I said earlier, Batrider is not item-dependent, so Linken's is a good choice.

--Late game? Do whatever you want. Facing casters ? go for sheepstick/orchid. Make Bkb if you are facing disablers. The main requirement that should be provided by items is - survivability. You now have enough mana to cast trillion times Sticky Napalm as the 20 mana will be restored before the cooldown is over. You are entirely free to buy whatever you want. I will suggest you only one thing - Upgrade your PT to BoT - for better lane control.

--At early game lasthit as much as you can. Rush Urn + PT + Perseverance. Spam Sticky Napalm, stack 4-5 times and then cast Firefly, cast Urn on the weakest enemy and rush your enemies. If you are careful enough you will kill the heroes you lane against. Use Flamebreak to ensure at least 1 kill. Gank other lanes if needed.

--Start to roam. You already have Force Staff - Gank as much as possible. When ganking cast Sticky Napalm 2-3 times, cast Urn, cast Firefly, cast ult and push yourself with Force Staff closer to your allies. If it's possible - upgrade your PT to BoT. Tp each time a big wave is available. Stack 4 times Sticky Napalm and then Flamebreak.

--This is the period of the game where you are not that useful. Try to push a lane and finish the game. Build BKB and bravely go next to a enemy hero and lasso it, bring him next to your allies and kill him. When teamfight happens - spam Sticky Napalm and rush through the battlefield with Firefly.