I have a question in regards to abilities, powers, and traits and how they should work, what limitations they should have, and ways to avoid meta-gaming/power play. For those unsure about those two terms, here is a brief description:

[indent][b][color=f26522]Metagaming:[/color][/b] Metagaming is when a player applies OOC-retrieved information to their IC character, such as your character hearing whispering because you saw the text, or knowing a character's name because you saw their username. This is the most commonly broken rule of role-play and most infuriating for many. 

[b][color=f26522]Power Play:[/color][/b] Powerplaying occurs when a player operates someone else's character without the other player's consent. Not only is this not fair to the other player, but it's also discouraged because often players will misconstrue the behaviours and personalities of characters they didn't design.[/indent]

Taking those into account, here are some the abilities that I have in question. responding and expanding to other examples would be greatly encouraged as I know that there are many others that I haven't thought of.

[pre]The Power of Hallucination:
This ability can be cast by a spell, magic, or other form to cause another player to see things that are not there.
Some of the questions I have about this ability include...
1: Due to this altering the way another character sees things, is this a form of power play?
2: If the ability changes the landscape, how would that change the world they interact with?
3: If the ability creates physical hallucinations, does that create concerns with Meta-Gaming and those viewing from the outside?[/pre]

[pre]Poison:
Inflicting poison onto another character.
1: Would this be an ability that can be viewed as overpowered, especially depending on the various strengths of a poison?
2: Should all poisons have an antidote and what would happen if you have an ability that doesn't have one?
3: Could this be viewed as Power Play as you are forcing other characters into situations?
4: How could you enforce a strong poison in a game without it becoming something that turns a character into a micro god/goddess?[/pre]

[pre]Mind Reading:
Ability to read the thoughts of others or even view into their memories.
1: Pretty sure this is easy... Is this Metagaming?[/pre]

[pre]Mimicking:
The ability to copy another player's abilities.
1: Similar to Mind reading... Is this Metagaming?
2: What happens if the abilities have to be learnt over time? Does that mimic player learn at a different rate?
3: What happens if it breaks the power entirely?
(eg: Copies the ability to use fireballs, writes a scene with the control of fire lava, Mimic player is told that Lava control was not part of fire control)[/pre]

Like I said, this is only a few examples and I'm sure others have many more, but I'm generally wondering how as someone who has played and GM'ed these situations, how would you go about in regulating this?