We could call these Scene Powers as a group
The term ‘encounter’ is a normal 5e term. By itself, it refers to anything the adventuring party meets.
But the term ‘combat encounter’ specifically refers to ‘a clash between two sides’, organizing into a ‘cycle of rounds and turns’ that begins ‘when everyone rolls initiative’ (PH 189).
So, it seems appropriate to refer to these powers as ‘per combat encounter’, abbreviated ‘• combat’:
action • combat
For 5e terminology, ‘per long rest’ is standard, but there are awkward situations where it is necessary to say ‘per day’, such as for elf Trance.
Analogously, ‘per rest’ (short or long) is standard, but there can be situations where it is necessary to say ‘per combat encounter’.
In 4e, the player was responsible for the narrative of a power effect, occasionally narrating the reactions of the hostiles to the effect. Thus both the DM and the player told the story of the scene. In 5e, the player narrates the character only, while the DM narrates the world around the character.
It seems to me vital for each power to include a narrative in its description that rationalizes the effect.
The ‘trick’ is a great example of a narrative explanation. The hostiles in a combat encounter fall for it once, but are unlikely to fall for it again.
If so, the power might work better to mechanically target the Intelligence defense. A particularly intelligent hostile is less likely to fall for the trick. And a less intelligent one more likely.
This suggests to me, a low Intelligent creature might fall for the same trick twice in a combat encounter. Maybe mechanically, the ally can keep on repeating the same ‘per combat encounter’ power on future turns until some hostile succeeds against it, or until the ally chooses to use a different power for ones action.
The ‘trick’ is mainly a mental attack analogous to a ‘feint’ action to Help an ally, a Deception skill or a Charm or Illusion.