This will only work for the poison wyvern on vannaheim. Before the mouth of the cave there is a slit in the wall. Put a foundation to get up into it. Put a chest in the back safe and sound. Build a thatch foundation. Sloped roof. Wall. And ceiling and build it right below the first nest to the righthand side of the cave. Once you grab the egg run out the nest and out the cave. Put the egg in that chest in the wall and come out and let the dragon kill you. Bam you have an egg.