First of all, Congrats! Accenture M&A Strategy is a great place to be!

In general Accenture interviews follow the PEI + case interview format. The main difference when applying to a practice-specific position is:

1) Be prepared to deep-dive in your experience in M&A Strategy
- Prepare stories that show your experience in M&A Strategy, and how these experiences can help you at Accenture
- Why do you like M&A Strategy

2) There is a greater chance that your interviewer is from M&A Strategy, hence there is a greater chance that your business case will be about this topic, but not necessarily 
- Prepare yourself for M&A Strategy cases, not only how to approach but recent trends can be a plus to connect with your interviews
- Prepare for non- M&A Strategy cases, many times the interviewer has shelf cases that do not practice-related and/or he believes test your skills better.

3) Think about what questions and topics you can bring in the interview to reinforce your commitment with the practice

-  Recent trends of M&A Strategy
-  M&A Strategy career specific questions

Accenture's skills interview is very relaxed, conversion based. Dont become too formal or come across as too rehearsed. Go with the flow, talk about your experience (in M&A), skills, ambitions and ask good questions. They will most certainly want to know your background, industry experience and have clarity on where do you think you want to go. 

Prepare a good answer for “Why Accenture”.

All the best.