None of your revisions are correct.
Student or Learner
Adverbs of completeness: When adverbs of completeness or manner go in mid-position, they are normally put after all auxiliary verbs
- I have completely forgotten your name.
- Sally can practically read it.
- It was almost dark.
English Practical Usage by Michael Swan, p. 23-26.
I would like to ask if we can put 'adverbs of completeness' at the end and the beginning of a sentence or not.
- I have forgotten your name(,) completely.
- Sally can read it(,) practically.
- It was dark(,) almost.
(P.S. I am not sure if I should put comma before those adverbs or not)
- Completely, I have forgotten your name.
- Practically, Sally can read it.
- Almost, it was dark.
'I have forgotten ... completely' sounds O.K. to me. Is it unnatural?
"I have forgotten your name completely" is a natural, correct English sentence. The others aren't.
***** NOT A TEACHER *****
I have found some sentences that may interest you. They come from a grammar book that is highly respected.
1. "He denied it completely." (That is, "He denied it in very respect.")
2. "They divided up the money completely." (That is, "the whole of the money"; the experts say that many people would NOT accept: "They completely divided up the money.")
3. "He didn't ignore my request completely, but he did ignore it to some extent."
4. "He drank up his beer completely." ("up" is necessary in that sentence.)
5. "He completely denied it" means something like "He strongly denied it." But "He denied it completely" means "He denied it in every respect."
-- Quirk, Greenbaum, Leech, and Svartvik, A Comprehensive Grammar of the English Language (1985 edition), pages 590 - 596.
I also found something that might interest you:
"Hey, great you could make it [able to come], hm..., I hope I haven't forgotten your name completely, it's Ye ..., Mya, I know. Ye Mya Sung, am I right?"
-- from a novel entitled Barren Sand by Heinz Ross (accessed through the "books" section of Google).