Imprisonment is D&D 5e 9th lvl spell. It, nomen omen, imprisons single creature by chaining it, burrowing it and so on. Here is how to implement it in OL:
- you need a 3rd tier in Heightened Invocation,
- be able to invoke Immobile Bane,
- in addition, you need to invoke Absorb Object if you want to lock creature IN some object.
There is also home rule needed that enable casting Heightened Invocation first, then spending 1 day to rest/stabilise.
All you need is to immobile target creature, then you can leave it where it stands or lock it in gem or miniature cage.
Heightened Invocation is probably the right way to go here, although I’d make it easier for myself.
I am familiar with the Spell, and I think merely using Heightened Invocation III to make the Immobile or Incapacitated Bane (depending on version of the spell) permanent captures the feel very well, even though the details like casting time are a bit different. You can easily allow an ending condition, maybe the GM even requires one.
The rest is just flavour, such as being portable etc., though it’s reasonable to say access to Absorb Object is required to lock the target in an object rather than the earth or a place.
Heightened Invocation definitely has a lot of room for extra effects like this, it’s a great way to add a bit more flavour to your rituals. As always with powerful effects though, a GM needs to be cautious that the party don’t just lock themselves in a tower and use it to solve all their problems with no conflict; be sure to occasionally throw them a curveball by telling them they’ve run out of a rare ritual ingredient, or a rival mage is interrupting them with his own Heightened Invocation - Nullify or something else to keep it interesting.
I don’t really think that’s much of an issue, because you need to have reliably captured your target anyways, Heightened Invocation III takes some time after all. There is also already the trade-off, making the Immobile Bane permanent is quicker but doesn’t prevent interaction.