So the Mark only works on 1 creature per short rest? But scales better?
Not quite.
Since I’m combining the two ideas, it’s developing quickly as I discuss it.
Assassin’s Mark v1: starts at 1d10 2 times a day, scales up to 10d10 10 times a day at level 20.
That would be insane on top of half casting and extra attack, BUT.
Assassin’s Mark v2: Costs a spell slot, and scales by spell level. you can cast it once without a spell slot. This scales up. I am still working out the wording.
Basically, you have enough [USES] per day to cast it at your current highest spell level twice, but you don’t have to cast it at the highest level. So if you are level 17, you have 10 [uses], and you can spend them however you want. Level 1 ten times, level 5 two times, anything in between.
The exact numbers may change. Probably will. That is a lot of extra “spell slot” equivalents.
As for what the mark does.
At level 1 it grants advantage to checks to track, search, or examine, the target, and you add your intelligence modifier to damage against the target. You can end the spell to deal 2d10 extra damage on an attack when you hit. Every spell level adds 1d10 to that damage.
It isn’t a spell, and it doesn’t scale automatically. That is, at level 5 you gain the ability to spend a second level spell slot to deal 3d10 when you invoke the mark, and at level 9 you gain the ability to use a 3rd level slot, etc. so you can’t dip into the class and get the full progression.
Eventually you gain crit on a 19-20 against your Mark target, which dovetails with being stealthy for advantage. At level 5 you gain Deadly Precision to drop to 0hp any target you drop to less than twice your assassin level HP, and at 11 you get a feature that makes a single target save or die if they are CR [x] or lower.
The rest of the class is all about stealth, special tools, using terrain, mobility, and weird esoteric mysticism.
Assassin v1 has ritual spells but no spell slots, but 2024 makes that not needed, and I can just give the class the spell list that serves its needs.