Each of those permanents that is a creature at the time your declare attackers step begins must attack its owner if able
They enter untapped, provide good fixing, and have few downsides
Alternative Art pricing is driven entirely by IP appeal and art quality
I looked at the all, and I think I've played all but three of them at some point in time in my game playing days, as it's my 2nd favorite color combination to draft for Abedraft (a draft I have of every card ever printed save for around 15 that are too pricey to pickup)
Golgari Grave-Troll Golgari Grave-Troll, like Dread Return, is a Legacy Dredge mainstay
Ive calculated all of these on a per-slot basis, so then this table has those odds x2, due to the pair of potential slots