Lines 108-119 seem to determine some extra score that you can collect when properly following your path. I haven't been digging deep in that now, so lets forget about it for now and look at it afterwards.
Lets assume now we did everything correct. So after line 127, our @xmas_reward_tally could be 35. And now the disconcerting part: At line 130, @xmas_reward_lower_bound is calculated to 70-rand(5). At line 133, @xmas_reward_upper_bound is calculated to 70-rand(5)+LUK/5 Then in line 134 @xmas_reward is finally calculated as a random. It could be any value from 66 to 75.
The desired Level-Up reward is finally determined in Line 157 (@xmas_reward_tally_rare also being a constant value of 80). So our @xmas_reward must be 80 at least to get the Level up. But it is in the range of 66-75.
To get it to 80, we have to get the initial @xmas_reward_tally to 7 at least, in Lines 105-119, before adding the 35 from all helpers and boss fights. If we had it at 7, then the lower bound would calculate to 2*(7+35)-rand(5), thats a value in the range 80....84. And we would be fine.
How to get it to 7? I haven't exactly found out yet and wiki says there is a karma system but not in use. But wiki might be wrong. Assumed the karma system is in use, then I have to speak out a warning:
Do not do the Boss fight for the path that you are NOT following, this might lower your Karma and destroy your chances for a Lucky Level up.
Its late and I will be playing less next weeks. Somebody else might dig any further in this karma stuff.
A quick search for locations from where the karma is set revealed: Everytime when you do the xmas daily, your karma is increased by 1 for nice / decreased by 1 for ugly path. There is a hard limit of 15 for nice / 0 for nasty. So, do the christmas daily every day if you can.