Seeing as it’s a day of suggestions it seems… we are lacking path obstacles, as we only have one type of thing to impede movement along the path. Soooo
New obstacle - PIT OF HADES
Covers a single square, acts mainly as a slow down of troops and hero. Also deals damage proportionate to it’s lvl.
Some units are slowed less, such as siren/phoenix, etc. Some are slowed more trebuchet, spearman, etc.
I would put this as a type of tower choice rather than barricade type choice otherwise it would make raiding even easier than it is already.
This should appear as a semi phased opening to the underworld, showing the hands/upperbodies of souls imprisioned in hades clawing at the hero/troops as they pass over. Scary stuff. Image as a starting point to get an idea