testing procedure:
set up curses on blasphemy & eye of malice (should put enemy at -284 cold resistance)
kite a single bloodstained warrior until theyre alone
place a single lvl1 wintertide brand (wintertide does exact same amount of damage every time)
wait for all damaging effects to expire
check their hp
repeat but with an extra -res curse on blasphemy (should put enemy at -384 cold resistance)
compare hp values
repeat but with no eye of malice and just one curse (should put enemy at -189 cold resistance)
compare hp values
results:
with -189 cold res, the enemy hp stopped on the right part of the d in "blood"
with -284 and -384 cold res, the enemy hp stopped on the left part of the d in "blood"
enemy resistance is almost certainly capped at -200 just like player resistance