Hi! I'm the moderator for Repton (https://www.speedrun.com/repton1), which I added to the site yesterday. I don't expect this game to get much attention, but would like to populate it with my own records so that they are there for others to challenge :)
Level 11 (Giant clam) is a concern, because this level plays out completely differently depending on whether you accept losing a life, or complete it with one life. If you accept losing a life, you can do the lower half first, which lures the monsters into a safe place so they won't disturb you during the upper half. To illustrate how much difference that makes, my current best time for the level is 2:34 one life, 2:07 losing a life.
Obviously it would be nice to separate these two runs. However, for the majority of levels in the game, "1 life" doesn't make any sense as a category because best times will be done on one life anyway. So, is it possible to have an IL category for just this one level, or should I maybe add "Giant clam (1 life)" as a separate IL?
Defining the same level several times as separate ILs is not a good solution. That's what categories are for - playing levels but in different ways. For this case you should use a subcategory, and make it unique only to your relevant level. That means, add a new variable with values for life, mark it as subcategory, and set it only for level 11.
An example of that is the IL leaderboard of Celeste - Level 1 A-side specifically can be done with dashes or without dashes, and that changes the game play. Making a full category of "no dashes" is not good, because no other level can be beat without dashes. So they added a relevant subcategory only for level 1.
That being said, I'm curious about why would you want to separate this level 11 for "losing a life" and "not losing a life.". If one way is faster than the other, then most likely all runners will choose the faster one, no? Still it's your choice.
(By the way, you still need to make an IL category for all levels, like "Any%" or "Competed". Without that no one can submit ILs.)