The fight with the Titan is all about the proper reactions to the attack patterns described below. It requires dexterity but you shouldn't have too much problems if you can keep up with the things happening on the screen.
White runes keep showing up on the floor. From the moment the rune starts to blink white you have around five seconds to move to another block. After that the block will disappear, leaving a hole in the floor. After another five second the block will appear once again and other ones will disappear, so keep an eye on the floor all the time.
When the enemy move one leg forward, it means that he'll attack with an energy beam. Avoid it by running in the opposite direction.
The Titan will use this each time you get too close to him (and randomly too, as well as the others). He crosses his "hands" and raises his right leg. Once he lowers it - jump to avoid the wave.
When the enemy summons white missiles that surround him, you should quickly use the shield of the Titan Lord. There are two variations of this attack. The missiles will be launched one after another or next to each other. Reflecting the missiles (and hitting the Titan) will allow you to attack.
The only way to damage the Titan is to stun him (lasts for around 5 seconds) with his own missiles (see Magic missiles) and then hitting him with the hammer of the Titan Lord. He falls after receiving 7 hits. Follow this patter and eventually you will see Risen's ending credits.