This is a usually a fun-filled scenario but the secondary deck mechanic can misfire in one of two ways:
Mugash ends up on the top of one of the secondary decks and so is revealed early (often ending in catastrophic loss)
Mugash is on the bottom of one of the secondary decks in a long slog where the board state id prepared for his appearance, but you have to slog away where everybody's bored, just waiting for the blasted card to show.
To avoid these drawbacks build your secondary deck as follows:
1. Play 5 cards from your deck facedown onto the table.
2. Take the next 10 cards from your deck and shuffle Mugash/bodyguard into these cards. Place these cards facedown on top of those dealt in step 1
3. Top the deck with 5 more cards from your hand.