Blue Crawler has almost no point in being used, that's what.
It is a 3/3 for 3. That is very comparable to a 5/5 for 5 (entropy), 3/3 for 3 (death), etc. It's common to see a trend like this, taking into consideration that life gets cheap creatures, earth gets high health creatures, and so on.
And so, I just don't see what the problem is. The only thing I would say is that, for cost, the toadfish is probably better, because it has more attack than its cost, and its health increase isn't proportional, but since it exists, it can survive a hit from any source that deals 3 damage. However, if we are to compare like that, the shrieker looks better than the golem, and the mummie gets a lot of power for little cost over the flesh spider, so even that seems fair.
The 3/3 for 3 has web
The 5/5 for 5 has a decent damage.
Then, shriekers are OP, do not use them for comparing.
And again, flesh spiders' web can be really used.
3/3 for 3
has an ability that uses
and currently takes a specific shield to be useful.
5/5 is decent damage, sure, but that doesn't make a card good, does it?
Would a 5/5 for 6 be better than a 3/3 for 3? I would, personally, say no. Why pay 6 for 5 damage when I could pay 6 for 3 damage. Even facing a shield that reduces damage by 1, they are equal damage.
5 damage is good for the 5 cost.
Why is 3 damage not ok for the 3 cost?
Would it be worth it if we gave it an ability like this?
Dense Bones
The enemy creature acts as if it had 5 HP for the purpose of shields. Actual health is unchanged.
It would then be better than web, which affects only a shield with a set amount of time before disappearing, and the costs, damage, and health are exactly the same. It would seem like a silly change to me, since I doubt people would start using water/gravity decks anymore than they currently use death/air (or the phase spider for aether/air to use the web ability), but if that is what is missing for this to be a good creature, ok, I wouldn't stand against a buff that I would see as fairly meaningless.