What version are you using - this is in 1.10
/setblock ~ ~1 ~ minecraft:mob_spawner 0 replace {SpawnData:{id:"customnpcs.CustomNpc",Pos:[1214,56,879],StartPosNew:[1223,56,879,],MovingState:1,WalkingRange:10,ReturnToStart:0,Texture:"customnpcs:textures/entity/humanmale/Evil_Gold_Knight.png"},SpawnPotentials:[{Weight:1,Entity:{id:"customnpcs.CustomNpc",Pos:[1214,56,879],StartPosNew:[1221,56,879,],MovingState:1,WalkingRange:10,ReturnToStart:0,Texture:"customnpcs:textures/entity/humanmale/Evil_Gold_Knight.png"}},{Weight:1,Entity:{id:"customnpcs.CustomNpc",Pos:[1214,56,879],StartPosNew:[1221,56,879,],MovingState:1,WalkingRange:10,ReturnToStart:0,Texture:"customnpcs:textures/entity/humanmale/FireSteve.png"}},{Weight:1,Entity:{id:"customnpcs.CustomNpc",Pos:[1214,56,879],StartPosNew:[1219,56,879,],MovingState:1,WalkingRange:10,ReturnToStart:0,Texture:"customnpcs:textures/entity/humanmale/RobesBlackSteve.png"}}],SpawnCount:1,SpawnRange:10,MinSpawnDelay:10,MaxSpawnDelay:100,MaxNearbyEntities:10,RequiredPlayerRange:30}