The recent change to arena mixed up the monsters a bit... like in the 3rd part, in the last wave of mecha knights you often find several devilites hiding in there. It introduces new challenges, but by bad luck it could also turn very ugly.
Yesterday I solo'ed 2 arenas with hearts and pills left unused all over the place, but today it was very painful... the last few waves of the 3rd part were:
Alpha wolvers (shock)
Jelly turrets (shock)
Mecha Knights + Mender + Devilites (shock)
With the removal of the blind spots on turrets, fighting those alpha wolvers was a nightmare. You can't block - alpha wolves will break it immediately and shock you. You can't run properly - jelly turrets will all be shooting once you circle the arena once, and their spikes were so slow, they leave very little safe place for you to move. And the fact they were all shock-themed. Once you got hit once, you will suffer more hits due to the shock. So much pain.
The devilites hiding among mecha knights are also a huge problem. If they were the normal version you could just trade some hits to deal with them, like what people do with menders... but with shock? You can't risk it, or you will be shocked and then surrounded by mecha knights, followed by a swift death.
I think some combinations are too deadly... I think they should limit the list of possible choices, say the devilites mixed in can only be the normal version, or increase heart drops for such combinations.
I think I'll avoid shock-themed arenas for now...
What was the arena theme?