Even after examining this card's art, I'm not
sure whether the idea is that the sentry becomes
an Eldrazi or is just preventing one from
emerging. But if it's the latter, why doesn't it
just go around or over him (seeing as most
Eldrazi are huge)? And why would the Eldrazi in
question join your side? I wouldn't hold that
against the card, though - I think it could
actually turn out to have a niche in
constructed. At the very least, its
power/toughness ratio with delirium active could
make it a sort of Pauper Tarmogoyf. That format
is also known for having surprisingly powerful
removal spells, and creature decks can pretty
much always use more insurance on that front.
This card is interesting. It's normally
undercosted for its body (3 mana 1/2 cards with
little board impact), but it's a lot more
powerful later in the game with delirium online.
A 3 mana 4/2 is a lot nicer as an attacker or
blocker, and delirium is pretty achievable
overall.
The other side of the coin is that it replaces
itself when it dies, which gives it use early
and late. A 3/2 is a pretty good replacement for
a 4/2 (or 1/2). So it gives you a bit of
resilience to board wipes or targeted kill
spells.
It's also a Human, and Humans in this block have
a lot of powerful support. So, yeah. Solid
common in Draft, and I can see scenarios where
it sees constructed play.