A Decker's Matrix avatar is automatically created based on his or her "meat-world" appearance. Every three turns a decker's avatar takes in the cyberspace equals one turn the rest of the party gets in "meat-world". (Things moves faster in there!) While the deckerís consciousness is running around cyberspace, his body is inert in the real world and the rest of the party needs to defend him until he returns. To exit a Matrix LAN, the decker needs to leave from the same portal he entered or eject and suffer dumpshock damage to his physical body.
As the deckerís avatar navigates a Matrix LAN node, it will encounter Intrusion Countermeasures (IC) which will attack him. To fight the IC, the decker uses computer programs and deploys ESP Ė Expert System Programs Ė which are "independently operating artificial life simulations". ESP operate under the player's control and each has its own abilities.
The decking skill is used to derive the deckerís "to-hit" calculation and the ESP subskill determines the power of his ESPs. The deckerís cyberdeck determines how many and what level of programs can be taken into the Matrix. There are a variety of different programs for attack, defense, buffing, and debuffing. The cyberdeck is also the deckerís first line of defense Ė damage the decker takes is first applied to the deck which has its own equivalent of health points called IP. But Black IC or attacks from enemy deckers can damage the decker directly.
Every Matrix LAN has an alarm threshold and every action the decker takes within the LAN moves him closer to that threshold. When an alarm is tripped, it might trigger the arrival of Black IC, an enemy decker, or bad things back in the meat-world.
With all the danger inherent in cyberspace, why go there? Because the Matrix LAN nodes can control things in the meat-world like doors, security cameras, automated turrets, security clearances, and even poison gasses flooding into room. And, of course, the Matrix holds the most valuable thing in the 6th world Ė information.