The US based social games maker Zynga has signed $20m agreement to acquire California-based game maker A Bit Lucky in a bid to attract more serious gamers.

Following the completion of the transaction, A Bit Lucky’s all the 20 employees will join Zynga’s San Francisco division.

The acquisition reveals Zynga’s transformation towards mid-core offerings, the titles which will that sit between highly produced, packaged games and relatively basic ‘casual games’ including Words with Friends and FarmVille.

The transaction also follows Zynga’s hiring of John Tobias, a co-creator of the "Mortal Kombat" series, for operating a new mid-core title.

The transaction will also support its product line during the decline in number of users for even its most popular online games like "FarmVille" and "CityVille".

Zynga is also involved in allegation with its competitor Electronic Arts, which sued Zynga against unfair copying of elements of EA’s "Sims" game.

In a counter statement, Zynga accused EA of violated a deal between the two, which limited Zynga’s hiring of employees from the other firm.