Thing that makes text scale in on the y-axis.

JonEffect.cs

using UnityEngine;
using System.Collections;
using TMPro;

public class JonEffect : MonoBehaviour
{
	TextMeshProUGUI text;

	[Range(0f,1f)]
	public float buildInPercent = 0;

	void Awake()
	{
		text = GetComponent<TextMeshProUGUI>();
	}

	public void Update()
	{
		buildInPercent = Mathf.Clamp01(buildInPercent);

		var textInfo = text.textInfo;

		text.ForceMeshUpdate();

		for(int c = 0; c<textInfo.characterInfo.Length; c++)
		{
			var charInfo = textInfo.characterInfo[c];

			if(!charInfo.isVisible) continue;

			int matIndex = charInfo.materialReferenceIndex;
			int vertIndex = charInfo.vertexIndex;
			var verts = textInfo.meshInfo[matIndex].mesh.vertices;

			Vector3 midPoint = (verts[vertIndex + 0] + verts[vertIndex+2])/2f;
			Vector3 size = verts[vertIndex + 2] - midPoint;

			float percentPerChar = 1f/(float)textInfo.characterInfo.Length;

			float charPercent = c * percentPerChar;

			float squashY = Mathf.Clamp01((buildInPercent-charPercent)/percentPerChar);

			size.y *= squashY;

			verts[vertIndex + 0] = midPoint + new Vector3(-size.x,-size.y,size.z);
			verts[vertIndex + 1] = midPoint + new Vector3(-size.x,+size.y,size.z);
			verts[vertIndex + 2] = midPoint + new Vector3(+size.x,+size.y,size.z);
			verts[vertIndex + 3] = midPoint + new Vector3(+size.x,-size.y,size.z);

			textInfo.meshInfo[matIndex].mesh.vertices = verts;
		}

		//NOTE: ideally you don't want to update the geometry every frame, so you could disable this when the build-in is complete. 
		for(int m = 0; m<textInfo.meshInfo.Length; m++)
		{
			text.UpdateGeometry(textInfo.meshInfo[m].mesh,m);
		}


	}

}