While it's nice that you are thinking about "spoilers" carefully, I think these sort of minor spoiler warnings cannot coexist with the presentation of data we have here. I mean, it sort of already fits on one page here.
Also, keeping the boss of Stage 4 a spoiler and revealing the boss of stage 5 is not very consistant. I either recommend no spoiler warnings anywhere (leave the Spoiler warnings on the Imperishable Night page), or add a screenfull of blank space between Playable Characters and Enemy Characters.
--Leviathean 15:39, 29 Apr 2005 (PDT)