Stripped oil plug
If you use a good pair of vise grips you may be able to get it off if you adjust the visegripes just beyond your ability to clamp them and then proceed to clamp them shut with a large pair of channel lock pliers, if this does not work drill the appropriate size hole through the bolt and tap in a large easy out bolt extractor into the hole drilled and proceed to use a star socket
on the end of the extractor to unsrew the frozen oil pan bolt.
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