Thank you for bringing up the topic!
I came across these 5 most common ways to pierce a corporate veil:
1. The existence of fraud, wrongdoing, or injustice to third parties.
2. Failure to maintain the separate identities of the companies.
3. Failure to maintain separate identities of the company and its owners or shareholders.
4. Failure to adequately capitalize the company.
5. Failure to follow corporate formalities.
More details in reference: https://www.lexology.com/library/detail.aspx?g=4ff8ebf0-4bca-426e-8273-758140f6d0eb