I’ve got an idea for your !lastkill command:
Have another bot with a count variable (ie. Ankhbot) join the channel and make sure the streamer has added it as a moderator.
Assuming you’re familiar with Ankhbot custom commands, you can set up a command on Ankhbot called !addkill such that after Nightbot has added an entry to the kills list, Ankhbot will respond with “!editcom !lastkill (whatever text you want here) $(urlfetch http://twitch.center/customapi/quote?token=(YOUR_QUOTE_TOKEN)&data=(ANKHBOT_COUNT_VARIABLE))”
What this essentially does is change the entry ID search in the !lastkill quote API every time someone uses !addkill
Make sure to make the Ankhbot !addkill command moderator-only.
This may not work if Nightbot can’t react fast enough to different commands in such a short time.
Let me know how it turns out!