Hunting the Rathian! The Rathian should be the first wyvern that you can encounter during the storyline or even in the online tavern. She is a rather soft wyvern to begin with having her head as the weak spot for shot types so if you can snipe her head precisely, this fight will be quite easy but if you want to break the wings you may also do so as this will make her stagger and fall to the ground when she is in flight mode.
She has seven(7) different types of attacks when grounded. The single fireball, triple fireball, step back ground fire ball, tail back flip (can poison and stun) that will always make her go to flight mode right after, a 360 tail swipe, full on head charge (may vary if she uses triple charge or just a single one) and a bite that doesn't do a whole lot of damage even for gunners.
While she is on flight mode she has four(4) different attacks. The dual bite lunge, the tail back flip (a lot of times she does this twice), the diving claw that ends up pinning the hunter down when it connects and a forward bite attack that does little damage. She always roars when she goes enraged and back hops flying.
RANGED TACTICS:
Bowgun
Its main elemental weakness is dragon while the secondary one is thunder. As a gunner, you can easily break her out of flight mode by staggering her whilst she's in the air. Pierce shots on bowguns are strong but beware of the recoil because it will plant you down and gives less time to recover. Keep moving to one side preferable to the left when she's grounded and to the right when in flight. When using the HBG use the roll to widen or close the gap between you and her, just keep a close eye on your stamina bar. The LBG that has a thunder/dragon rapid fire capability can do large amounts of damage in short bursts.
Bow
If you're good at precise aiming for the head and other weak parts, Rapid bows are good. Elemental bows are strong if you use the 2nd and 3rd stage of the charge pair this up with a good level 3~5 scatter bow and you're good to go. Bring coatings that your bow can use, though the bow may lose the elemental damage when a status coating is applied, a good paralyze or maybe sleep coupled by a couple of barrel bombs+ can do massive amounts of damage just be sure to hit the bomb and not the monster when it's asleep.
MELEE TACTICS:
You can use any melee weapon you're not limited to the list below.
Gunlance
Guard +1 can easily neutralize all his attacks. When you want to duke it out, use that guard stab and follow it up with an upswing. Upswings are fast, strong, versatile attacks, you can do several upswings while avoiding left or right, the upswing animation cannot be interrupted by the Rathians wind pressure. When tripped, use the longest combo you can do while using the shelling in between for maximum damage output.
Switch Axe
Most Switch Axes can get a huge buff from power phials when in sword mode, the axe mode's upswing has the most vertical reach but be warned that this may launch fellow Blademasters in the air when in multiplayer so be aware of the reach. Most dragon Switch Axes can only be unlocked at G rank so your bet is using thunder types at the early get go. With the vertical reach this has, knocking her out of the air and cutting her tail off will be easier. All of the Switch Axes attacks negate Rathian's wind pressure.
Dual Blades
Fast! Fast! Fast! coming in and going out of the her attack range is crucial, if you can avoid her attacks without getting hit and exploiting small openings then the Dual Blades is a weapon for you. What it lacks in attack range makes it up with its quick agile attacks. When Rathian's in flight mode, you can clip her tail end and proceed to knock her out of the air. You can also focus your attacks on her legs as she can be easily tripped and then proceed to Demon Dance away at her HP. Evasion +1 can help you avoid most of her attack, you can also roll over her fireball if you time it perfectly with Evasion +1. While in Demon mode wind pressure is negated so another thing to keep in mind.
Don't forget to bring:
1. Flash bombs (you can knock her out of the air)
2. Traps (when monster is fatigued)
3. Bombs (sleep bombing)
4. Combination materials (extra coatings/ammo)