What is defeat an enemy that has a titan skill?

Titan skills are not all that rare, in fact it was released as part of a free content pack in Infinity Blade III: Soul Hunter. Titan skills are more commonly known as "Boss Perks".

Titans at level 100 or higher may have Boss Perks. The higher the level, the more likely the Titan will have a Boss Perk. You can tell if a Titan has a Perk by clicking the info icon on the bottom right of the screen before battle. The Boss Perk will be listed, along with any elemental attacks and resistances it has.

The following was added so as to ramp up the difficulty of the game. Here is a youtube video with more information about the content pack and "Boss Perks".

Here is also a list of different types of Titan Skills and what they do:

Immune to Magic

• You can’t use magic in this fight – not even to heal yourself!

Immune to Super

• You cannot use your Super Move against this Titan.

Elemental Titan

• This Titan is immune to all elemental damage and delivers Darkfire elemental damage, which can’t be defended against!

Great Parry Only

• Normal parries have no affect! You must perform Great Parries or Perfect Parries (you can also block and dodge).

Perfect Block Only

• Normal blocks cannot defend against this Titan. If you choose to block, only a Perfect Block will do the trick.

Normal Damage Resist

• The Titan takes very little damage from non-elemental attacks. Use strong elemental attack gems for this one!

Super Fast Attack

• The Titan attacks much faster than usual.

Reference: LINK