I’m surprised that when an enemy is Entangled, in my case by Sylvanimora, Warhound’s spell to reduce the enemy’s attack is ineffective. I understand why, though. Since an Entangled troop has 0 attack, Warhound can’t reduce it any further.
But you’d really want Warhound to reduce the enemy’s actual attack so it doesn’t return to full strength when the Entangled wears off.
I suppose you have to imagine that the enemy’s sword is wrapped up in vines, too, so can’t be snatched away…
On the flip side of that coin, attack-buffing spells and traits also do not function while Entangled. The buffs are ignored, even after Entangled wears off.
Interesting. I hadn’t noticed that before.
And then there’s devouring an Entangled ally, which of course grants the devouring creature (eg Black Beast) none of the base Attack stat of the troop devoured.
I notice all the time when my Treant is Entangled. 
The armor buff works but the attack buff doesn’t; I try to save casting his spell until the Entangle wears off.