First of all.To do this,you must have a strider or else it doesn't work.To make it work you have to run HlaPEx.exe and then run your lineage2 server.
After you enter the game with the char that has the strider in the inventory,you open HlaPEx and choose the sniffer directory.
Then you hit the capture button and return to your lineage2 server.
Now summon your strider and ride it.After riding it return to HlaPEx and hit Stop.Now you have to find the client side packet named "ride" and hit "Copy To ->" button and then choose advanced or Copy To 'Send'(in newer version) option.
Almost every server has fixed this exploit so each time you ride your strider the client side packet is different,never the same ,so you'll have to do this proccess each time you enter the game.
Now that you have the packet "ride" in "Advanced"or"Send(in newer HlaPEx version)" directory you are able to ride a strider without summoning it just by hitting "Send" button.
Let's get to the point now.The packet of the strider you have Will look like 86xxxxxxxxx100000001000000xxxxxxxx.
All you have to do is to change it to 86xxxxxxxxx100000002000000xxxxxxxx and you can summon the Wyvern.Remember to send the packets from HlaPEx -> Client.
The summoned Wyvern can only be seen by you.It's Client side.You can use it to do whatever you like.I just enjoy my flights around Aden.
This exploit is tested and works on TheGame PvP server,MML2 servers,Infogate.I am sure it should work in all private servers.Just test it and post.
Remember:you must have a strider or else it doesn't work.(you can buy it or raise it as i did) :)