* His ult is on equal grounds with Void's chronos. It stuns in an AOE, also reveals invisible (the invisible has to attack the target), it has a farther casting range, it causes damage by making enemies attack each other.
* He is a nuker and a healer and a DPS at the SAME time. That is a rare combo on its own. There are INT heroes which you can make DPS with item choices to give damage b/c they might come with IAS such as Lina and Ogre. However, many people overlooked Arctic Burn as a natural DPS (it does % HP damage), which is "better" than Naix's passive especially being ranged, or "super" ranged. He is a natural tank killer.
* Comes with 2 natural slow and an AOE stun, what a freakin' combo! And his heal turns your teammates into tanks or support your current tank with the extra armor. And he is an effective farmer to level faster and getting items faster.
The first incarnation of Wyvern, he gets flight vision during Arctic Burn (like Batrider's flight), that made him completely OP. They since changed it, so now you don't have that vision anymore and require a tank or wards. It's a good nerf, else he is ultimately the best hero in the game. You're still laughing at me.
Hero Guide to Winter Wyvern:
Winter Wyvern is an INT hero and often played as a pure support. Most common known as a Geo killer, but he can devastate any team easily from afar. He is a healer, lane controller, nuker, stuner, slower, DPS and could even tank if necessary though probably better to use Cold Embrace on your teammates to make them tanks. The most effective way to play him is actually DPS build, which makes him a RARE all around hero that is an INT. His BEST game is actually lategame.
Support Wyvern:
This part is included just because I have to. You can get a meka to stack his heal or guinsoo/orchid to support. Basically play him like any other support, but it makes no sense b/c unless you can get items to match his abilities, they're just random. Item choices are selected to build up your hero's abilities. So this is generic, cliche, and good early carry to mid, lategame purely support.
DPS Wyvern:
To play Wyvern effectively, you build the hero around Arctic Burn, his key ability. Most people in support builds it around his ult, some getting refresher, etc... However, Arctic Burn (AB) is a HP % DPS, like naix. It tears away enemy heroes from a super far range. Because Wyvern is an INT, you want to get him IAS items. AB is time limited, so you want to get in as many hits as possible in that time.
Early Game: First 15-20 minutes
I know I said I don't like soulring, but this is like the 3rd hero I'm recommending this item. Remember, I generally recommend soulring when you need regn and tread. Yes, Wyvern needs tread for bulk and IAS. The soulring + RoA is again more than enough for this hero if you play him right early. Someone actually asked me that in the game how I was able to play him with only a soulring. Eventually you'll need skadi, which will give you all your mana needs. But that shouldn't be your first major item.
Wyvern is a long range hero and in early game is a support b/c your IAS is too low. Everything about him is range, so don't initiate, don't stand in the front. Use the soulring and Splinter Blast (SB) to farm creeps. He is an effective farmer and can level fast and get gold fast.
Build your skills: AB, SB, SB (start farming with it at level 2 SB), Cold Embrace (at level 4, before that use your tango), SB, ult, SB (level 4 splinter blast is ultimate farming), AB all the way then finish CE. CE even at level 1 is good enough early so level it last. But if your team needs a stronger healer, finish CE first as AB is good lategame.
Items: STR Tread, Soulring, RoA for early. Your first core item is actually SnY. SnY is one of the items I rarely get b/c it is a level 2 items and in most cases I don't like low level items for lategame. However, this is the exception. WW's one weakness early is slow movement. And since also need IAS, SnY is the ideal choice. The maim will also give you a 3rd slow and the extra HP helps you bulk up a little. If you are having trouble, such as a Spectre or SA harassing you even when you are in the back, a BM or a ghost is recommended though those items must be sold later for IAS items. A Lothar might be more appropriate since it comes with IAS. However, those are emergency items if you need them, not the recommended items for a late build.
Mid Game: 15/20-30/35 minutes
By mid game, you should have the early game core item SnY. At this point you have a choice. If you are doing well, your next item is maelstorm and turn into mjolnir. This will help you farm. SB should be cast on a melee creep, it will automatically kill the range but leaving other melee creeps weaken. The maeltorm helps you finish that. Also, you need the IAS and it also gives you some damage.
The next item is skadi, but if you needed more bulk, skadi could come before mjolnir. In previous versions, skadi will give you a 4th slow stacking on AB. In the updated version you do not get this frost. However, it is still a key item b/c it gives you bulk, manapool, and the stats themselves gives you damage, armor, etc... and of course, it gives you IAS. At this point you have mjolnir, tread, SNY, and skadi. All 4 items that gives you IAS. You are a formidable range DPS with AB.
Strategy: At this point, you should be enough to do some IAS damage. This is midgame, so your nukes are still good and your ult is still good. But with the IAS and mjolnir, you are very capable of handling yourself and supporting your team. You can cast mjolnir on yourself if you are being harassed or cast it on your tanks as they lead. Mjolnir cast on your tank with CE is quite effective.
Late Game: 35 min +
By lategame your last 2 item choices should be 1 more IAS and then 1 damage. You can go 2 more IAS if you wish, but I like to have 1 damage to stack his tank killing AB. My preferred IAS is butterfly. Why? Because you are already tanky enough with skadi and SnY for an INT hero, but just in case you get harassed or in trouble with flank heroes, a butterfly helps you sustain a fight even without AB. A cuirass is not recommended, because the armor reduction range for cuirass is not far enough for AB to help you. Another good IAS item would be orchid, giving you a silence ability. Take your pick on any of these.
The final item, which I recommend a damage item, is actually abyssal blade. Rarely is range bash good, but in this case, you are a hero with 5 IAS items, that bash is crucial when the enemy tries to TP away or a Geo trying to poof away. It also gives 100 damage, higher than other weapons.
At this point with full items, you are virtually unstoppable and you almost never require your ult at all, so save it. Your AB is so freakin fast you can take down any tank in a few seconds. WW is all about range, the best range ability is SB. Cast and spam SB into the enemy and when your team fights, use AB to take out the tanks and CE to heal your tanks. When necessary, use your ult. If you see a silencer or something, ult that first, instant kill. Never ult their DPS, use them to kill their own teammates.
Geo Killer
You've probably heard this before, how WW can destroy Geo. This is in context to using the AOE stun and his teammates killing the Geo. However, Geos can actually survive the ult if they're bulky enough and kill you. Geo's rarely get DPS and they rely on their collective damage to kill. Also, lategame Geo is rich and what if he BB and you're ultless? If you build WW from this guide, you can solo Geo without your ult. To this date, I cannot think of a way a Geo can counter this WW build. Perhaps that is why WW is missing from EdgeofChaos' Geo guide on how to counter Geo's counter. There simply isn't one.
Example:
This is a real game I played against EdgeofChaos' frightening Geo. I actually didn't know it was him until some times later he posted a replay with the same account on an unrelated game. Now, this isn't a me vs him thing, it is a team game of course. However the one example I wanted to use was just the last few minutes of the game.
This Geo was one nightmare for our team and the only advantage we had was the other 4 players on his team were terrible. Also, because he did so much, pushing, farming, laning, his teammates didn't get to grow or farm well. Regardless, this Geo alone killed our team again and again and destroyed both the Bot and Mid rax. So in the final moment of the game and my WW is maxed out with the items above. He came top to finish the rax while his teammates split pushed to keep the pressure on the 2 other lane.
My teammates were split defending mid and bot when Geo showed up top, as per Geo strategy to use your teammates as distraction. I splinter first, remove his blink ability, then I ult, then I arctic blast him. In a mere few seconds I killed him. My teammates successfully defending mid and bot and pushed the creeps out. During the fight with Geo top, I also cleared the creeps. It was already a good 50 min to 1 hr, I guess either he got tired of carrying his noob team or he thought that since I'm ultless and we were down a few heroes, he could TP top and finish us off.
So Geo tp top and push into the rax again, I was ultless. However, both SB and AB were CD. I splinter, prevent him from blinking, then AB a Geo to death. It really didn't matter which Geo I got and with the bash, he couldn't poof or do anything. In this game, I remember specifically he went 3 skadis, probably thinking he can out tank the ult. But remember AB is % damage, it really didn't matter how much HP you got, it tears you down the same. What mattered is how many times you hit them with AB.
Geo dies the 2nd time and can't BB. My teammates pushed mid to their rax, I defended then TP with BoT to join them and we throned, took the game.
Conclusion:
This example will work on ANY team, not just Geos. This is why Wyvern is perhaps the single most underrated hero of all time. He's not just a Geo killer, he's just a killer. Of course though he has his counters too. He hates Specs, SAs, and flank heroes. He can still get overwhelmed by a team of heroes alone without his ult. But in most cases he is formidably dangerous and overlooked. Perhaps being overlooked is one of his greatest advantages. Your enemies won't know what is coming.
I would love to see more WW players out there.
Skills: AB, SB, SB, CE, SB, ult, SB, AB all the way then finish CE.
Items: Tread (BoT), SnY, Skadi, Mjolnir, Butterfly, Abssyal Blade
5-10 yrs ago, my speed was much closer to EdgeofChaos. He reminds me of a young me. 
You guys boasting and comparing about how good you are, you have no idea you're not anywhere near the levels I've played and seen. But so what? Look at me now, whenever there are too much action on the screen? My eyes go oogly 
and my hero just auto attacks.