Mordenkainen's Faithful Hound?

[Segev]

I think there is potentially more trouble than just this in the spell. The hound only attacks hostile creatures within 5' of the caster. You may literally have to stand next to it and, dm ruling dependent, it may not be able to attack things on the opposite side of you. Anything with reach can be immune to it's attacks by simply not being adjacent to the caster.

In addition since the hound can't take the hide action the common interpretation of stealth says that everyone knows there's an invisible thing in that space.

Now, this is from the internet, but unless that's wrong, it attacks foes within 5' of the HOUND, not the caster.

Yeah, the foe just needs to be within 5 ft. of the hound and hostile to the caster. Nothing about needing to be within 5 ft. of the caster.

[Telok]

Ok, my bad. Apparently I've been reading it wrong. I think it still suffers the invisible creature radar issue tho, which means you need a method of forcing enemies into position for the start of the caster's turn. But I think Segev covered that one.