Damage Numbers Pro

First you need to create a new damage number.
Click on the + symbol in the Hierarchy window.

Mesh: 2D or 3D Worldspace (no canvas)
GUI: Canvas Rectspace

I recommend saving your damage numbers as prefabs in a shared folder.
Makes access and organization easier.

If you save the damage number in a scene instead, keep it's gameobject disabled.

You can customize everything within the damage number inspector.
Use the tab buttons to navigate through the settings.

Everything is structured into features.
Click on a feature to toggle it.

The [R] button resets the feature and the [?] button displays hints.

You can use preset buttons to customize faster and find new possibilities.

You can also edit the material and text mesh pro settings.
Simply click the tab buttons to view them.

If you picked the Mesh version you will see the popup in the editor.
The GUI version has to be in a canvas to render.

Visual settings (text, material & tmp) will update while editing.
For other settings you need to play your game to view them.

Hint:
To tweak other settings you can edit the prefab at runtime.
Spawned popups will use the latest prefab settings.

Mesh Example

The script below will spawn a random number between 0 and 100 on leftclick.

using UnityEngine;
using DamageNumbersPro;

public class Example : MonoBehaviour {

    //Assign prefab in inspector.
    public DamageNumber numberPrefab;

    void Update()
    {
        //On leftclick.
        if(Input.GetMouseButtonDown(0))
        {
            //Spawn new popup at transform.position with a random number between 0 and 100.
            DamageNumber damageNumber = numberPrefab.Spawn(transform.position, Random.Range(1,100));
        }
    }
}

Simply assign a damage number prefab to the numberPrefab variable.

Leftclicking will now spawn a random number between 1 and 100.

GUI Example

The script below will spawn a random number between 0 and 100 on leftclick.
Popups will be children of rectParent with an anchored position of (0,0).

using UnityEngine;
using DamageNumbersPro;

public class Example : MonoBehaviour {

    //Assign prefab in inspector.
    public DamageNumber numberPrefab;
    public RectTransform rectParent;

    void Update()
    {
        //On leftclick.
        if(Input.GetMouseButtonDown(0))
        {
            //Spawn new popup with a random number between 0 and 100.
            DamageNumber damageNumber = numberPrefab.SpawnGUI(rectParent, Vector2.zero, Random.Range(1,100));
        }
    }
}

Simply assign a damage number prefab to the numberPrefab variable.

Leftclicking will now spawn a random number between 1 and 100.

using DamageNumbersPro;

//Basic:
DamageNumber damageNumber = numberPrefab.Spawn();
DamageNumber damageNumber = numberPrefab.Spawn(Vector3 position);
DamageNumber damageNumber = numberPrefab.Spawn(Vector3 position, Transform followedTransform);

//Spawn and Set Number:
DamageNumber damageNumber = numberPrefab.Spawn(Vector3 position, float number);
DamageNumber damageNumber = numberPrefab.Spawn(Vector3 position, float number, Transform followedTransform);

//Spawn and Set Text:
DamageNumber damageNumber = numberPrefab.Spawn(Vector3 position, string leftText);
DamageNumber damageNumber = numberPrefab.Spawn(Vector3 position, string leftText, Transform followedTransform);

DamageNumber damageNumber = numberPrefab.Spawn(Vector3 position);

//Set Followed Target:
damageNumber.SetFollowedTarget(Transform followedTransform);

//Set Color:
damageNumber.SetColor(Color color);

//Set Gradient Color:
damageNumber.SetGradientColor(VertexGradient vertexGradient);
damageNumber.SetGradientColor(Color topLeft, Color topRight, Color bottomLeft, Color bottomRight);

//Set Random Color:
damageNumber.SetRandomColor(Color from, Color to);
damageNumber.SetRandomColor(Gradient gradient);

//Font Material:
damageNumber.SetFontMaterial(TMP_FontAsset font);
TMP_FontAsset font = damageNumber.GetFontMaterial();

//Set Scale:
damageNumber.SetScale(float scale);

//Prewarm Pooling (call this once):
damageNumber.PrewarmPool();

DamageNumber damageNumber = numberPrefab.Spawn(Vector3 position);

//Set Parent and Anchored Position relative to rectParent
damageNumber.SetAnchoredPosition(Transform rectParent, Vector2 anchoredPosition);

//Set Parent and Anchored Position relative to rectPosition
damageNumber.SetAnchoredPosition(Transform rectParent, Transform rectPosition, Vector2 anchoredPosition);

//Set Parent and Position to Mouse Position (canvasCamera as null if canvas is Screen Space - Overlay)
damageNumber.SetToMousePosition(RectTransform rectParent, Camera canvasCamera);

DamageNumber spawnedPopup = popupPrefab.Spawn(...);

public IEnumerator CountDown()
{
    //Spawn a new popup.
    DamageNumber spawnedPopup = popupPrefab.Spawn(transform.position);
    
    //Make the popup permanent, so we can fade it out manually.
    spawnedPopup.permanent = true;
    
    //Changes within the popup's first frame do not require the UpdateText() function.
    spawnedPopup.number = 3;
    spawnedPopup.numberSettings.bold = true;
    spawnedPopup.SetColor(Color.yellow);
    
    //Loop until the popup is zero.
    while (spawnedPopup.number > 0)
    {
        //Wait 1 second.
        yield return new WaitForSeconds(1);
        
        //Decrease number by 1.
        spawnedPopup.number--;
        
        //Lerp color towards red, as the number reaches 0.
        spawnedPopup.SetColor(Color.Lerp(Color.red, Color.yellow, spawnedPopup.number / 3f));
        
        //Update the text of the popup.
        spawnedPopup.UpdateText();
    }
    
    //Wait 1 second.
    yield return new WaitForSeconds(1);
    
    //Fade out the popup.
    spawnedPopup.FadeOut();
}

//These modify the displayed texts and number.
spawnedPopup.number = floatValue;
spawnedPopup.leftText = stringValue;
spawnedPopup.rightText = stringValue;
spawnedPopup.topText = stringValue;
spawnedPopup.bottomText = stringValue;

//These toggle the displayed features.
spawnedPopup.enableNumber = boolValue;
spawnedPopup.enableLeftText = boolValue;
spawnedPopup.enableRightText = boolValue;
spawnedPopup.enableTopText = boolValue;
spawnedPopup.enableBottomText = boolValue;

//Sets TextMeshPro's color.
spawnedPopup.SetColor(Color color);

//Sets TextMeshPro's color to a random color.
spawnedPopup.SetRandomColor(Color fromColor, Color toColor);
spawnedPopup.SetRandomColor(Gradient gradient);

//Enables and modifies TextMeshPro's vertex gradient.
spawnedPopup.SetGradientColor(Color topLeft, Color topRight, Color bottomLeft, Color bottomRight);
spawnedPopup.SetGradientColor(TMPro.VertexGradient vertexGradient);

//Changes TextMeshPro's font asset.
spawnedPopup.SetFontMaterial(TMPro.TMP_FontAsset font);

//Returns TextMeshPro's font asset.
TMPro.TMP_FontAsset font = spawnedPopup.GetFontMaterial();

//Returns an array of the popup's TextMeshPro components.
foreach (TMPro.TMP_Text tmp in spawnedPopup.GetTextMeshs())
{
    //Mesh popups return 1 component, but GUI popups return 2.
}

//Makes the popup follow a target and add its instance ID to the spam group.
//The ID prevents popups, of different targets, from interacting with each other.
spawnedPopup.SetFollowedTarget(Transform target);

//Sets the scale of the popup.
spawnedPopup.SetScale(float scale);

//Sets the position of the popup.
spawnedPopup.SetPosition(Vector3 position);

1. Open the Game Creator.zip file included in the asset.
2. Open the Version 1 or 2 folder depending on your version of Game Creator.
3. Always extract the Basic.cs file but only extract the Stats.cs file if you use the stats module.

Note:
- Extract Version 1 into the Game Creator folder.
- Extract Version 2 into the Damage Numbers Pro folder.

There are 2 custom instructions (or actions).
Read below to find out which one to use.

Important:
Drag your damage number prefab into the Prefab field.
Only dragging works for some reason.

Open the Playmaker.zip file included in the asset and extract it.

There are two custom actions you can choose from.
The Spawn Popup action should be easier to use.

Spawn Popup: Spawns a single popup whenever the state is entered.
Auto Spawn Popup: Spawns a popup whenever a specified variable changes.

In both cases you first need to drag your prefab into the prefab field.
Prefabs contain pretty much all the settings of your damage number.
You should have a prefab ready after following the Create and Customize section.

Auto Spawn Popup

Changes to the checked variable will be detected.
Depending on the conditions a damage number will be spawned.

The state has to remain active to spawn new popups.
May need it's own separate PlayMakerFSM and a Get Fsm Float action.

Additionally you have the option to use the detected change as the number.
So you can automatically spawn numbers whenever an entity is damaged (or healed).