This is Magic's representation of the
hekatonkheires (literally the hundred-handed
ones), giants who joined Zeus' rebellion against
Kronos in Greek mythology's creation stories.
Personally, I have yet to block a hundred
creatures at once with this card, but that's so
far outside of Magic's normal experience that
you can see how they helped Zeus win the war.
His stats are very solid and the monstrosity
upgrade comes at just the right time to keep him
relevant against Titans and dragons. I also love
how monstrosity interacts so well with popular
casual cards like Doubling Season.
Theros had many callbacks to Greek mythology,
some of them obscure. This is based off of the
hecatoncheire, a hundred-handed monster. And
that is what it is here (after going monstrous).
4 mana for a 3/5 with vigilance isn't
unreasonable; it blocks and attacks quite well.
For 6 mana, you can turn it into a 6/8 with
vigilance and reach and the ability to block one
hundred creatures each combat, which sounds
cooler than it actually is. It's basically a
large, hard-to-kill cudgel that can stop a
lethal swing in a pinch.
Unfortunately, it has no real protection besides
its high toughness, so it's not as good at
blocking as you'd hope, but it can do the job
well, especially in Limited.