Guild Hall ★8 (G-Rank - HR5): Water Wyvern of the Jungle - Ganostoo Strong, Crafting a Great Sword

I just can't beat him... Ioedrome is also there constantly getting in the way, so I absolutely have to take him out first. But by the time I deal with him, I run out of ammo and time, and I still haven't beaten the main target.
There's a spot on top of a cliff where you can shoot him safely, but the Vespoids that spawn right next to you are endlessly annoying. In the end, I tried using a light bowgun several times, but I couldn't pull off a win.
To dodge Vespoids, fighting in close quarters actually works because you're constantly moving around, making it easier to avoid them. Fighting up close has pretty predictable patterns which make dodging attacks manageable, but close quarters usually means using Spread Shots.
It's just a repetitive cycle of dodging his breath attack and striking, dodging and striking. At that point, I started thinking: wouldn't a melee weapon just be better for this?
So I looked into it. Fire-element weapons require a ton of rare Rathalos materials, which sounds painful. Another effective element is Thunder, and the Thunder Great Sword 'Ogre Cutter' looks promising.
First, I needed Khezu Electro Sacs and Lightning Sacs. Electro Sacs come from normal and hard rank, while Lightning Sacs are G-rank, so I hunted that red Khezu I hadn't fought yet.

Crafting a Great Sword from scratch is quite a challenge. Whether it's just this specific sword or Great Swords in general, it uses an insane amount of Earth Crystals. Maybe it's because they're huge? Earth Crystals are probably used to forge steel and stuff. Also, I needed tons of Caelite Ore. To get all these, it was time to mine in the Volcano.

To mine efficiently in the Volcano, I equipped the 'Gathering +2' skill to increase the number of mining swings.

After a few mining trips and collecting minerals at the farm, I finally crafted the Ogre Cutter.
Just you wait, Cephadrome—I mean, Gypceros—no, Gendrome—wait, Gendrome? Ah, Gypceros! No, Ganos! Just wait, Plesioth! I'm going to slice you into three pieces, roast you with electricity, and eat you!

By the way, because I couldn't beat him no matter what, I actually went to hunt a Diablos first before making the Great Sword.

By making sure not to break its horns and hitting its body with Pierce Ammo, the fight becomes much easier to manage. If the horns are broken, it charges left and right randomly, making it really hard to line up shots. But Vespoids are super annoying here too. Basically, I had to wipe out the Vespoids with Spread Shots and squeeze in some shots in between, or just run around constantly while spamming Pierce Ammo.

The second, black Diablos was exactly the same. Make sure to bring Sonic Bombs just in case. Still, having this many back-to-back hunts against the exact same monster is way too much—what on earth was Capcom thinking back then?

