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.

Lagorin, Soul of Alacria

Flying
Whenever Lagorin attacks while saddled, put a +1/+1 counter on each of up to two target Mounts and/or Vehicles.
Saddle 1 (Tap any number of other creatures you control with total power 1 or more: This Mount becomes saddled until end of turn. Saddle only as a sorcery.)

Caradora, Heart of Alacria

When Caradora enters, you may search your library for a Mount or Vehicle card, reveal it, put it into your hand, then shuffle.
If one or more +1/+1 counters would be put on a creature or Vehicle you control, that many plus one +1/+1 counters are put on it instead.