/summon minecraft:zombie ~ ~ ~ {Passengers:[{id:"minecraft:horse",Tame:1,ActiveEffects:[{Id:14,Amplifier:0,Duration:2000000000,ShowParticles:0b}]}]}

/summon minecraft:zombie ~ ~ ~ {Passengers:[{id:"minecraft:horse",Tame:1}]}

/summon minecraft:ender_dragon ~ ~ ~ {Passengers:[{id:"minecraft:horse",Tame:1,ActiveEffects:[{Id:14,Amplifier:0,Duration:200000000,ShowParticles:0b}]}]}