This isn't a bug issue, but one thing I think that could be done with Horde mode is to make the blocking mechanic more needed. In that game mode, I was able to basically survive by just collecting the hearts and the lightning bolts. If that's your intention, then that's fine. I just think that making the block mechanic more necessary in that mode would increase the variation in the Horde mode. This is just my opinion on it. Other than that, Horde mode is really fun and I really like the gameplay!
There is another thing I found that might need to be fixed.
In one of the areas of the map, there seems to be a hidden wall. I don't know if that is intentional or not, but I think it should be fixed. Another bug I ran into is that when I was fighting one of the rock guys when he had lost both of his hands and he was red, he just simply stopped near one of the pillars.
Edit: It crashed and brought up this error:
___________________________________________
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FATAL ERROR in
action number 1
of Other Event: User Defined 2
for object Golem:
Variable Golem.clap_offset(100300, -2147483648) not set before reading it.
at gml_Object_Golem_Other_12
############################################################################################
--------------------------------------------------------------------------------------------
stack frame is
gml_Object_Golem_Other_12 (line -1)
called from - gml_Object_Golem_Step_0 (line -1) - <unknown source line>