The command works on single player, but for some reason it doesn't work on the server.
Command:
/summon minecraft:sheep 74.5 77 -27.5 {CustomName:"\"BOSS\"",CustomNameVisible:1,Glowing:1,CanPickUpLoot:0b,Health:1,Attributes:[{Name:"generic.maxHealth",Base:1}],Color:0,DeathLootTable:'{"pools":[{"rolls":1,"entries":[{"type":"item","name":"minecraft:wool","weight":1,"functions":[{"function":"set_data","data":0}]}]}]}',HandDropChances:[2F,2F],HandItems:[{id:"minecraft:white_wool",tag:{display:{Name:'{"text":"\\u041a\\u043b\\u044e\\u0447"}',Lore:['{"text":"\\u041c\\u043e\\u0436\\u0435\\u0442 \\u0431\\u044b\\u0442\\u044c \\u0438\\u0441\\u043f\\u043e\\u043b\\u044c\\u0437\\u043e\\u0432\\u0430\\u043d \\u0434\\u043b\\u044f \\u043e\\u0442\\u043a\\u0440\\u044b\\u0442\\u0438\\u044f \\"\\u0441\\u0435\\u043a\\u0440\\u0435\\u0442\\u043d\\u043e\\u0439\\" \\u0434\\u0432\\u0435\\u0440\\u0438"}']}},Count:1},{}],ActiveEffects:[{Id:5,Amplifier:0,Duration:2147483647}]}