The card Bladecoil Serpent says When this creature enters the battlefield […] your opponent discards Y cards […].
When it discards, it discards from the first card in hand down to the last, until Y is met. This is a violation of the discard rule, which reads Cards that use the discard ability will, by default, discard the last card in hand […]. If it would discard any other card, it will be specified in the text (“Discard the first card”).
Bladecoil Serpent does not specify which card, so it is bugged.