Guide to Hidden Grotto Encounter Abuse
The encounter slots for Hidden Grottoes are in the 5th Gen Tools drop-down menu. This guide will use the first two tabs on the encounter slot page, which are titled D-Black2 and D-White2. The percentage value listed next to each individual Pokémon is the percent the encounter can be female. Note that this doesn't match the actual gender ratio. There are 11 slots (listed vertically) and 4 sub-slots (listed horizontally).
Every 256th step the player takes is when every unoccupied Grotto will run a check to generate, and they generate in the order listed on the encounter slot page. The order is VERY important. Unlike the 128-step counter, this step counter is not saved. If you've played through the entire game without ever visiting a Grotto it's a safe bet to assume they're all filled. EVERY Hidden Grotto listed before the one you want to RNG the encounter in MUST be occupied by either an item (hidden or not) or a Pokémon. This is EXTREMELY important. Also, make sure the Day Care is holding no Pokémon. Walking with Pokémon in the Day Care will advance the PIDRNG past your target.
You'll want to save inside the Grotto that you wish to RNG the encounter for. Have any Pokémon you may need (capture, sync, etc.). If it's occupied then take the item (which may or may not be hidden) or faint/capture the Pokémon prior to saving.
Sample Hidden Grotto Encounter Abuse / Using RNG Reporter in Hidden Grotto Abuse
The example this guide will use is RNGing a female Vulpix from the Grotto in Abundant Shrine (labeled as Abundant [Field] in the encounter slot page). First, a picture and then the explanation on how to use the searcher:
Slot: The 11 slots that are listed vertically. Vulpix is 0 so check it.
With that all filled out let's run the search:
You'll notice that you'll get a lot of results FAST. This is normal. Pick whichever one you like. The Hidden Grotto encounters are dictated by the PIDRNG, and all results in the Time Finder use the initial frame. This means you would simply boot your game at the correct time, walk 256 steps, and then exit and re-enter the Grotto. If you got the correct seed, your encounter will be there.
Getting the desired IVs
RNG abusing for the IVs is the same as for a stationary Pokémon, with a few exceptions. Firstly, Pokémon encountered in a Hidden Grotto cannot be shiny. Secondly, in the Capture tab 5th gen Time Finder, you must select Hidden Grotto as the encounter type. Thirdly, the main window has to be setup like this:
Take note of the Encounter Type, and more importantly, the Gender. In the Gender drop-down menu, you have to select the corresponding actual gender and ratio for your specific Pokémon. Since the example uses a female Vulpix, you would select (25% Male/75% Female). You MUST use the correct settings on the Time Finder and the main window or else you WILL get the wrong nature.
After that, the rest is identical to a stationary encounter. Since shiny is not possible, you will not have to advance the PIDRNG very much at all to get your desired nature.