Help Please

[billoloco]

18A : Multi-game equestrian event to display the talents both of horse and riders 8 Letters ??M?T???
17D : Mario ???R?T?I American driver who won the 1978 Formula One championship : 8 Letters
19D : Dog owned by cartoon star Dennis the Menace : 7 Letters ??A?H??
Thanks billoloco

[factor-fiction]

Gnasher

[shooty]

mario andretti

[shoota]

17d Andretti

[emmie]

17d think that mario andretti
19d gnasher

[boxtops]

17 Andretti
19d Gnasher

[factor-fiction]

Andretti?

[bookbinder]

19d Gnasher

[shoota]

18a Gymkhana

[dannyk13]

18a Gymkhana
17d Andretti
19d. Gnasher

[shooty]

gymkhana ?

[bibblebub]

18a) gymkhana - if the T is wrong

[snoopyfan]

Dog is Gnasher

[emmie]

eventing?

[billoloco]

Thanks everybody