How to find last date of the month in formula in salesforce

In this formula, I am using today's date you can replace your date.

Sample Formula

IF(
  MONTH(TODAY()) = 12,
  DATE( YEAR( TODAY()), 12, 31 ),
  DATE( YEAR( TODAY() ), MONTH ( TODAY() ) + 1, 1 ) - 1
)

Output

How to use custom metadata type values in Process Builder

In the Summer 19 release, Salesforce introduced the option to use custom metadata type values in process builder, formulas, and validation rules.

if you don't have pre-release dev org, sign up using below link
https://www.salesforce.com/form/signup/prerelease-summer19/

Syntax to use Metadata value in Formulas

$CustomMetadata.CustomMetadataTypeAPIName.RecordAPIName.FieldAPIName

Example
I created the Account_Generic_Data__mdt for this demo.

and created the Value__c filed on Account Generic Data Custom metadata type.
and I created the record

To Use this value in formulas and process builders
Example:

$CustomMetadata.Account_Generic_Data__mdt.Acc_Minimum_Amount.Value__c 

Resource:
https://releasenotes.docs.salesforce.com/en-us/summer19/release-notes/rn_forcecom_development_custom_metadata_process_builder.htm?edition=&impact=