As your minion is on a trip, it will automatically catch any implings it finds, provided it has the hunter level to catch them with a net (you don't actually need to buy a net).
You can view the collection log for implings with
There is a 1/85 chance of your minion finding an impling every minute of your trip, provided your trip is over 4 minutes in length and you're not completing the fight caves, inferno, ToB, or some minigames (Barb Assault, Castle Wars, LMS, Pest Control).
Each impling has a weighting that determines which impling you will receive when you do hit the 1/85 chance. The total of all weightings is 349 (if you have 89+ hunter). This means that each impling (except crystal) has a X/349 chance to be caught if you hit the 1/85, X being the specific weight of each impling type.
For example, (assuming you have 89+ hunter) you receive 1x Baby impling during your 30 minute trip. That means, you had 30 rolls at the 1/85 chance to find an impling, and you successfully hit the 1/85 once during your trip. The weight of a Baby impling is 66. That means, you then hit the 66/349 chance for a Baby impling.
The odds of catching a Baby imp every minute are 1/449 (the maths is: 1/85 x 66/349). Theoretically, you have about a 1/15 chance to catch a Baby imp every 30 minutes.
The chance of catching a Lucky impling is 1/29,665 every minute (1/989 every 30 mins).
* - Crystal implings are only available when doing activities within Prifddinas. This includes the Gauntlet, Zalcano, Killing Dark Beasts, or pickpocketing Prifddinas Elves.
** - Crystal implings have a static 1/155 catch chance every minute. This equates to about a 1/5 chance to catch a Crystal impling every 30 minutes.