How to increase size of Wither boss by using commands?

I want to make a map and in it a Wither boss that is bigger and more challenging. Is this possible using commands?

Solution 1:

No, it is not possible to change the scale of a mob in Minecraft: Bedrock Edition using commands.

However, you can create a behavior pack that will allow you to modify the scale, health and many other aspects of any mobs available in the vanilla packs using JSON data:

...
"minecraft:entity": {
    "description": {
      "identifier": "minecraft:wither",
      ...
    },

    "components": {
      ...
      "minecraft:experience_reward": {
        "on_death": "50"
      },
      ...
      "minecraft:boss": {
        "should_darken_sky": true,
        "hud_range": 55
      },
      "minecraft:damage_sensor": {
        ...
      },
      "minecraft:health": {
        "value": 600,
        "max": 600
      },
      ...

I have a tutorial over on Game Development SE that could get you started with creating your first add-on (which includes a behavior pack). Additionally, if you experience issues creating a behavior pack, I'd recommend asking any related questions on Game Development SE as they're currently considered as off-topic here.

_{Note: This answer is accurate as of version 1.17.11.}