Lyxen
Great Old One
I would agree with this one, in particular because it occupies its space. Although, actually, reading about it again, I realise that it's not specified. I wonder where that misconception comes from ? IN 3e it was spongy but was not specified to occupy a space, and it occupied its space in 4e, but nothing says so in 5e. So it may actually be fairly insubstantial and therefore not targetable.flaming sphere is another one that bugs me because it really feels like it's a physical object on fire