First you must attack it till it trys to limp away. Once it starts to limp put it to sleep with 2 bombs and place the trap under it. After that attack it so it fall in and that put it to sleep with two more. If it is still not traped attack it a few more times than put it back to sleep with your last two bombs. If you did it rigt it should be trapped and mission complete.
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My dragon has issues
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WARNING: "Next left" does not mean "turn left immediately."