Been trying to find some information about the ability of the Mark of the Shadow Elf and just wanted to see what the ability Slip into Shadow does. Here is what it states in the Race details:
Slip Into Shadow
You can use the Hide action as a bonus action, even if you have no cover or if you’re under observation. Regardless of whether you succeed or fail, once you use this ability, you can’t use it again until you finish a short or long rest.
I was simplying wondering what "Under observation means". Does it mean when an enemy is looking at you? Cause if that´s the case could you use it in combat?
Yes, "under observation" means that a creature is currently looking at the character. Also, there is no restriction on this feature about using it in combat situations.
As I understand it, this means that a Mark of Shadows Elf could indeed effectively hide in the middle of combat, without needing any cover to hide behind. Note that any character is able to attempt to hide during combat - all that is special here is that the Elf can do so without needing something to hide behind and can do so while being watched.
This ability lets you hide as a bonus action even when somebody is looking right at you. Let's look at two scenarios:
Scenario 1: Without Slip Into Shadow
To hide while being observed you must break line of sight with your movement then take the Hide action. However, even if your hide check is higher than their perception the person who watched you know where you went before you hid and would know where to move to in order to find you again or to get you with an AoE spell or something.
Scenario 2:With Slip Into Shadow
You can use your bonus action to hide even if being observed. If your hide check exceeds their perception you basically just disappear to them. You then have your movement to position yourself somewhere out of sight and can even use your action to dash and move farther (because while stealthing you can only move at half-speed) and they will not know where you went and therefore could not reliably chase you or target you with an AoE - they would have to guess. OR you could even get by them and use your action to attack - which will be with advantage because you were hidden.
This ability is absolute perfection for Rogues - with expertise in stealth, and especially if you get reliable talent - this is almost always giving you advantage and sneak attack on every turn.