Miriam, Herd Whisperer

During your turn, Mounts and Vehicles you control have hexproof.
Whenever a Mount or Vehicle you control attacks, put a +1/+1 counter on it.

Bucolic Ranch

{T}: Add {C}.
{T}: Add one mana of any color. Spend this mana only to cast a Mount spell.
{3}, {T}: Look at the top card of your library. If it's a Mount card, you may reveal it and put it into your hand. If you don't put it into your hand, you may put it on the bottom of your library.

Steer Clear

Steer Clear deals 2 damage to target attacking or blocking creature. Steer Clear deals 4 damage to that creature instead if you controlled a Mount as you cast this spell.

Holy Cow

Flash
Flying
When Holy Cow enters, you gain 2 life and scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Intrepid Stablemaster

Reach
{T}: Add {G}.
{T}: Add two mana of any one color. Spend this mana only to cast Mount or Vehicle spells.