This is how Mac trains the Skrill goes in A View to a Skrill, Part I.
[Then Mac breaks the iceberg and frees the Skrill]
Mac Grimborn: Just trust me, big fella. Please.
[Mac turns his head away and raises his hand as the Skrill touches it]
[The Skrill purrs at Mac as it lets him mount him]
[Then the Skrill flies in the air and does a barrel roll as Mac laughs]
[Hiccup watches and is impressed]
[The Skrill lands as Gobber arrives and puts a saddle on the Skrill]
[Mac gives the Skrill a name]
Mac Grimborn: Since you channel lighting, I'll call you... Sparky!
[Sparky roars in agreement]