A 10/10 that cant be chumped by smaller creatures is a great way to push damage through and finish a game, so, incidentally, is dealing 5 to each opponent every time you do
Now, you could use it to tap down a defense and swing, but thats not any better than Word of Binding
Sure, some Johnny somewhere will have a deck with a bunch of ETB triggers for Snare and friends to exploit, but until then, these are too much cost, for too little results
We included planeswalker deck walkers and a bunch of sweet legendaries that never got to see much play while they were in standard
UW Tron and 4C Gifts are two exceptions to this, although there is probably some unexplored space with other decks as well
If a permanent with an eerie ability enters at the same time as one or more enchantments, its ability will trigger for each of those enchantments