sudden juniper
nexon have remove iframe skill from game over the year
no more windmill iframe blaze iframe
people keep exploit skill iframe when u are supposed to do mechanic to kill boss
people skip theta crystal
people skip grandma fall sword
people use iframe to dodge many skill
is iframe what nexon want in game because they remove windmill and blaze iframe but not remove other skill iframe yet
undone stream
i-frames in Mabinogi are deliberately applied to relevant skills as a utility, and may be removed or altered for the sake of balance when the gameplay of that skill is changed!
Windmills i-frames for example were removed when windmills cooldown and hp reduction was removed.
Blaze's i-frames were removed when the skill aquired more range.
i-frames themselves are not bugs and were even intentionally added to more skills lately! Their intention is to be used to dodge attacks and get out of harms way.
Hope that helps! :)
If you do know of any glitches that occur as a result of i-frames, such as an enemy behaving abnormally, though, you may want to report that directly via support. :o
sudden juniper
then dodging isntat kill skill you are supposed to do mechaic properly is exploit
undone stream
I'm not sure. I dont run Glenn Bearna or Theta. 
If you think so, though, you can report it here. https://support-mabinogi.nexon.net/hc/en-us