My intention was to try to beat the game as just a thief if it was at all plausible and only upgrade to a ninja if I felt it was going to be needed to win. Having found out that Chaos has twice as much health makes me really think I'll need to upgrade to a ninja but I want to find out for sure with a little napkin math. I need to make this decision soon since in order to get all your ninja spells you need to make the switch by level 42. I'm currently 37 and I'm spending more time scumming for good levels than I am actually leveling since I can defeat everything on the peninsula of power and most of the monsters there don't run away yet. So, what does Chaos have going for him?
Chaos has 100 attack, 100 absorb, 200 hit, 1 crit, and 100 evade. He has 200 magic defense if I feel like casting terrible spells. Half the time he casts a spell from the following list in order: ice3, lit3, slo2, cur4, fir3, ice2, fast, nuke. Half the time that he doesn't cast a spell he uses a skill from the following list in order: crack, inferno, swirl, tornado. The remaining quarter of the time he melees twice. (Four times after he casts fast.)
Crack is an instant kill which I should be immune from since I will have a ProRing. Inferno has a damage value of 96 but is fire so with the ribbon I should always take normal damage from it. Swirl and tornado have damage values of 64 but will do double damage 68 times out of 201.
Ice3 does 70 damage. Lit3 does 60. Slo2 will blow out the thief 100 times of 201 but will just force the ninja to cast fast again. Cur4 is a full heal so I either need to burn him out before he gets around to casting it or I have to live long enough to burn him out after he casts it. Fir3 does 50 damage. Ice2 does 40 damage. Fast doubles his melee damage. Nuke does 100 damage and does double damage 143 times out of 201!
(Note that when a spell does 'X damage' it actually does damage between X and 2X. So Nuke could very well hit for 400.)
If he melees then he swings twice with 168+200 hit. On the NES this would actually be capped at 255 before taking my evade into account but on the PS he gets the full hit. My avoid is likely to be 99 so on the NES I'd get crit 1 time and hit 156 times in 201. On the PS I get crit 1 time and hit 200 times out of 201. That's right, even if I max my agility the 'hard to hit' character is guaranteed to be hit. I could use the shirt to max my avoid at 255 if I wanted to waste time (say, if my plan was to win after he heals to full) which would eliminate all normal hits on the NES and lower them to being hit 113 times instead of every time on the PS. My absorb will be 55 if I wear ribbon, proring, fire shield, opal bracelet. (Ninja only for the shield. I can drop 2 evade and 4 absorb as a thief.) So each time he swings on the NES he does 74 damage and each time he swings on the PS he does 95 damage. But when he attacks he swings twice (4 times after fast) so he actually hits me for 148, 190, 296, or 380 depending on game and haste status.
The expected damage from his spells/skills is 144 for inferno, 128 for swirl and tornado, 105 for ice3, 90 for lit3, 75 for fir3, 60 for ice2, and 257 for nuke.
So his attack damage is actually scarier than his spell damage. (Nuke can only be cast after fast.) These swings all have pretty high variance though, so I while I will get hit by everything I may just take low damage from most of it. But most likely, I'm dead in 7 or 8 damage actions. Probably I have to just burn him out before he casts cur4 (and therefore fast). So I get 7ish attacks to win, more if I get lucky and he attacks me a lot. (But not much more, since if he attacks me a lot I actually die faster.)
Is 7 attacks enough? Well, I'll have equipped masamune at this point. (Or maybe katana?) Masamune has 56 base attack. I will have 54 strength, so I get an extra 27 from that. So I will have 83 total attack. It has 50 hit, for a total of 153 hit and 5 attacks. It has a crit of 40 on the NES and 10 on the PS. Katana has only 33 attack and 35 hit but it has 38 crit on the NES and 30 on the PS. Also, for what it matters, only a ninja can use katana but a thief can use masamune.
Plugging everything into my spreadsheet I have total average damage on the NES with a masamune at 54 per swing. On the NES with a katana is 21. On the PS with a masamune is 34. On the PS with a katana is 17. I have 5 attacks per round so I need 8 rounds to win on the NES with a masamune, 24 on the PS with a masamune, and 47 on the PS with a katana.
I can live 8 rounds for sure and I can definitely get lucky enough to have 8 actions before the full heal, so I'm pretty sure I could win as a thief on the NES. There's no way to win on the PS as a thief. Even if I had infinite life his full heals would come more often than I could deal 4000 damage. Now, I could certainly get lucky with infinite health and get a long enough string of crits to win but the likelihood of that happening seems pretty small.
If I become a ninja then I can cast both fast and temper to boost my own damage. I could try to get lucky and cast slow, dark, and lock to try to make chaos weaker. I have items to use to boost my evasion and to heal myself. Fast alone reduces the number of rounds to kill him from 24 to 12. (+1 for the one to cast fast.) Temper adds 14 to my attack which alone would take me from 24 to 15. Put them both together and I'm winning in 8. This actually doesn't seem unreasonable. I waste two rounds to cast them both so I need to get a lot luckier than on the NES but it just could work.
The debuff spells are essentially impossible to land since Chaos has 200 magic defense and resists status. I think I'd hit 1 time in 201 when I roll a 0 and that's it.
But I don't think I need them. (I guess if I thought I did then I could try over and over to land my 1 in 201.) I am convinced I need to be a ninja though, so I cannot power level to 50 right away. I pretty much have to ding 39, kill Lich, and rush to the class change quest. I think I might be able to kill Chaos if I can pull that off. I just hope I can become a ninja and kill everything before him!