well this is confusing.

What does the larger and bolder "Use Item" do, the "Use on a pet" and the smaller "Use Item" all do?

Universal Remote is universal.

The larger-Use-Item is a menu that includes the use on a pet and feed a pet options. I don't think you can click this to do anything to the item per se, what it does is to open and close those options.

You can also small-use-item where you just use the item not-on-a-pet. It gives you items and sP if you small-use it this way.

I'm not sure what you mean by that. The feed a pet option is above the larger "use item", and the large use item is a link that goes to https://subeta.net/item.php?act=sp&itemid=3100321564 While the smaller use item goes to https://subeta.net/item.php?act=igiver&itemid=3100321564 while the "use on a pet" button is a dropdown which has all my pets with the urls containing the word "stat" so I assume this would be the stat increase option.

Going off the other two urls I will have to assume that the first one gives sP and the second one gives an item(s). It would be great if the staff could make it more clear though, given how rare/expensive the remote is I'm sure no one wants to misuse it.

The option to use on a pet should be the stat booster option, yeah. And I believe that is the option you're supposed to use to get the achievement, but I think I have seen at least one person say they did that and didn't get the achievement. If it's broken, it might be because of the changes made to the item menus somewhat recently.

If you're going for the achievement and use it on your pet but don't get it, I would probably file a ticket because the training/stat boosting option is supposed to be the one tied to the achievement.

(and I know having so many buttons is probably a tie-in to the item itself being a remote, but it does feel like the whole process for these is overly difficult lol)

sorry I missed your reply it does look my brain was scrambled there.

It could be that when the Item Box was re-done that the Universal Remote was not accounted for. It is the item that has the most kinds of use. The other reason to ask in Help is to see if it is a bug to report.