Mega Gyarados is a good switch into Bisharp.
252+ Atk Life Orb Bisharp Iron Head vs. 4 HP / 0 Def Mega Gyarados: 84-100 (25.3 - 30.1%) -- guaranteed 4HKO
252+ Atk Life Orb Bisharp Knock Off vs. 4 HP / 0 Def Mega Gyarados: 69-82 (20.7 - 24.6%) -- guaranteed 5HKO
252 Atk Mold Breaker Mega Gyarados Earthquake vs. 32 HP / 0 Def Bisharp: 248-294 (88.8 - 105.3%) -- 68.8% chance to OHKO after Stealth Rock
It's best if it is already megavolved though, because Intimidate gives Bisharp an attack boost in this circumstance. But a Moxie Gyarados still resists Iron Head and Knock Off does less damage from holding Gyarasodite still. Sucker Punch can be played around with Dragon Dance letting you get a free boost or two if he insists.
252+ Atk Life Orb Bisharp Iron Head vs. 4 HP / 0 Def Mega Gyarados: 84-100 (25.3 - 30.1%) -- guaranteed 4HKO
252+ Atk Life Orb Bisharp Knock Off vs. 4 HP / 0 Def Mega Gyarados: 69-82 (20.7 - 24.6%) -- guaranteed 5HKO
252 Atk Mold Breaker Mega Gyarados Earthquake vs. 32 HP / 0 Def Bisharp: 248-294 (88.8 - 105.3%) -- 68.8% chance to OHKO after Stealth Rock
It's best if it is already megavolved though, because Intimidate gives Bisharp an attack boost in this circumstance. But a Moxie Gyarados still resists Iron Head and Knock Off does less damage from holding Gyarasodite still. Sucker Punch can be played around with Dragon Dance letting you get a free boost or two if he insists.