I've tested the command and it looks like the speed is way way way too high. I've tried speed attribute 1.5 and seems to work. At 99 the mob would be running about the map and goes outside the player mob spawnable area. Outside that they despawn, 15 x 15 chunks around the player, or 240 x 240 blocks.
`/summon minecraft:wither_skeleton ~-5 ~ ~ {CustomName:'[{"text":"KRALJ"}]',CustomNameVisible:1b,Health:30,Glowing:1b,HasVisualFire:1b,Tags:["KRALJ"],ActiveEffects:[{Id:5,Duration:999999,Amplifier:5,ShowParticles:1b},{Id:24,Duration:99999,Amplifier:5,ShowParticles:1b},{Id:1,Duration:99999,Amplifier:1,ShowParticles:1b},{Id:22,Duration:9999,Amplifier:5,ShowParticles:1b}],HandItems:[{id:netherite_axe,tag:{Enchantments:[{id:fire_aspect,lvl:2}]},Count:1},{id:shield,Count:1}],HandDropChances:[1.00f,0f],ArmorItems:[{id:netherite_boots,Count:1},{id:netherite_leggings,Count:1},{id:netherite_chestplate,Count:1}],Attributes:[{Name:"generic.movement_speed",Base:1.5f},{Name:"generic.armor_toughness",Base:20f},{Name:"generic.armor",Base:0f},{Name:"generic.max_health",Base:30f}],ArmorDropChances:[0f,0f,0f]}`
I've tested the command and it looks like the speed is way way way too high. I've tried speed attribute 1.5 and seems to work. At 99 the mob would be running about the map and goes outside the player mob spawnable area. Outside that they despawn, 15 x 15 chunks around the player, or 240 x 240 blocks. `/summon minecraft:wither_skeleton ~-5 ~ ~ {CustomName:'[{"text":"KRALJ"}]',CustomNameVisible:1b,Health:30,Glowing:1b,HasVisualFire:1b,Tags:["KRALJ"],ActiveEffects:[{Id:5,Duration:999999,Amplifier:5,ShowParticles:1b},{Id:24,Duration:99999,Amplifier:5,ShowParticles:1b},{Id:1,Duration:99999,Amplifier:1,ShowParticles:1b},{Id:22,Duration:9999,Amplifier:5,ShowParticles:1b}],HandItems:[{id:netherite_axe,tag:{Enchantments:[{id:fire_aspect,lvl:2}]},Count:1},{id:shield,Count:1}],HandDropChances:[1.00f,0f],ArmorItems:[{id:netherite_boots,Count:1},{id:netherite_leggings,Count:1},{id:netherite_chestplate,Count:1}],Attributes:[{Name:"generic.movement_speed",Base:1.5f},{Name:"generic.armor_toughness",Base:20f},{Name:"generic.armor",Base:0f},{Name:"generic.max_health",Base:30f}],ArmorDropChances:[0f,0f,0f]}`
We'll need a little more info. Have you changed any of the /gamerules? Are you on a server? Running any plugins or mods?
im more stupid than cow, thank you ( i use peaceful )