Since it is generally believed to be impossible I took it as a challange to defeat all 4 enemies in mission 1 with Bastion.
This grants an extra ~200 XP and 3500 coins over the commonly employed strategy but relies on successful counter attacks.
I was able to get all 4 kills in mission one today, and IIRC all but 1 or 2 kills in mission 2.
I was not immediately able to reproduce all 4 kills in mission one so it must have been very RNG dependant. I had some savestates from the process and took a few screenshots but did not know exactly how i got to these savestates so there was missing RNG/steps that I may or may not attempt reproducing to varify if it's viable.
vague mission 1 sequence: 
save files to compare $$ between this stacked file and an average attempt:
this may not be RTA viable but I've been getting into this game pretty heavily the last week or so and so i figured I'd present my results in a public forum, since the records are all using the 3 kills strat from gfaqs.
Additionally, in regard to maximizing your XP gain you should always be using the strongest attacks available, even when the enemies HP is reduced.
I.E. Fireball will grant slightly more XP than Str. Slash, Str. Slash more than Slash, Slash more than kick, etc.
example: 
lasltly, in regard to the "99% miss rate" there is occassion when the RNG forces a miss regardless of context (target, attack, position, etc). the only way to change the RNG state (conjecture) is to attack (and miss) or use a support skill.
idk how active this game is but I saw schalakitty's run from last week on gdq.