Source: King Digital Entertainment 

King Digital Entertainment (KING.DL) will report earnings results today, marking the first earnings release since the company's IPO in March. Shares have fallen nearly 8% since listing, as investors continue to question the monetization abilities of social gaming companies like King and Zynga (ZNGA). And the first-quarter report could show further evidence of King's weaknesses.

What should investors watch in King's first-quarter earnings release?

Candy Crush dependency
In the pre-IPO paperwork, King revealed how much the company depends on Candy Crush Saga. The title accounted for 78% of total fourth-quarter bookings. It's not a bad thing for a company to have a runaway hit, but only if there's some decent-performing secondary titles as backup. 

King has existed since 2003 but didn't have a hit until Candy Crush released nine years later. A few post-Crush titles have gained smaller followings; Pet Rescue Saga and Farm Heroes Saga combined to account for another 17% of fourth-quarter bookings. But King's fortunes would reverse quickly if players turned away from Candy Crush.

Take a look at the growth of King's daily active users, or DAUs, and monthly active users, or MAUs. 

Source: King F-1 filing 

These numbers basically only show the growth of Candy Crush Saga over a two-year period. And that level of growth for one title is unsustainable for the long run because social gamers are fickle and a new best thing will soon come along. 

MAU growth between the second and third quarters was up 92%, but the growth dropped down to 13% between the third and fourth quarters. So check this week's earnings report for a further quarter-on-quarter shrinkage, because it could signal the warning bell for Candy Crush's demise. 

And there's two more numbers to check while examining the membership data.  

Monetization metrics
Two interconnected monetization metrics prove vital for social gaming companies: monthly unique players and the percentage of players making in-game purchases. 

Monthly unique players, or MUPs, refers to the number of unique players who have made game-related purchases over the course of a month. Since King and Zynga both deal in freemium games, the MUPs basically spell out how many people have made in-game purchases. 

Source: Company filings 

Zynga experienced a downslope but has steadier numbers overall. King experienced MUP growth right until the Candy Crush pullback in the fourth quarter. So look at King's first-quarter report to see if its losses continue. 

Another place to check for weakness is the percentage of players paying to play. Look for the monthly unique users, or MUUs, in the earnings release the calculate MUPs as a percentage of MUUs for the answer. King has stayed around 4% since Candy Crush took off, while Zynga tends to stay around 2%. Again, check to see if King's percentage dropped in the first quarter.  

Foolish final thoughts
Investors didn't flock to King's IPO, and the first-quarter results could further constrict share prices. Check the company's user and monetization metrics for signs that Candy Crush Saga is falling out of popularity. If that happens, King will have a serious money problem on its hands.