The power is a burst 1 that blocks line of sight for all creatures other than the warlock.
- What kind of attacks, if any, can target/hit the warlock?
- What happens if a monster attempts to attack the warlock from inside the zone?
Blocking Line of Sight functions as Total Concealment for the caster. Any creature attacking them takes a -5 penalty to their attack roll.
Attacks in general are not prevented by a blocked line of sight, so long as the creature still has Line of Effect. Attacks that are affected will specify in the attack description 'can see the target' or 'requires line of sight' etc. - examples include most teleportation effects.
Any creature attacking the warlock, whether inside the zone or outside it, will take a -5 penalty to their melee or ranged attacks. Blast and burst attacks are unaffected. Any creature within the zone (except the warlock) also takes that same -5 penalty when attempting to hit anything else, due to the blocked line of sight, and cannot teleport into or out of the zone. Any creature within the zone also cannot make opportunity attacks, as they require the attacker to be able to see the target.
- Any kind of attack can hit the warlock, except those that specifically require line of sight or to see the target.
- A monster that tries to hit the warlock from inside the zone takes a -5 penalty to its attack, unless it is a burst or blast attack.
For similar and possibly expanded information, see the answers to the questions on Stinking Cloud