Have done this one:
Type: ZOMBIE_HORSE
Display: '&aReh'
Health: 20
Damage: 8
Options:
PreventOtherDrops: true
PreventMobKillDrops: true
MovementSpeed: 0.32
Conditions:
onblock{m=GRASS_BLOCK} true
onblock{m=COARSE_DIRT} true
onblock{m=DIRT} true
onblock{m=DIRT_PATH} true```
But it does not spawn