Let's face it.
Blue Crawler is one of the weakest basic creatures around.
Basic creatures:
Abomination (survives to everything except a lightning, has a good damage.)
Mummy (Mummy is good, and gets crawler out). Flesh Spider (Has web, so, it's better).
Graviton Mercenary (one that can be compared to the crawler) Sapphire Charger (Better than crawler, better).
Hematite Golem (Survives everything, has a nice damage, and for only a quantum more).
Horned Frog/Cockatrice (What should I do? Better in every way compared to crawler).
Phoenix/Lava Golem (They both burn crawler down as damage.)
Pegasus (Better than crawler, certainly.)
Firefly and Wyrm (Again, Firefly can be compared, but Wyrm is more, MORE)
Vampire and Gargoyle (Better, way better)
Phase Recluse and Immortal (Horribly better)
doesn't have this creatures, maybe Anubis.
Toadfish (Toadfish is way more powerful than this)
Blue Crawler needs a good buff, now.
I think abyss crawler is REALLY strong when upgraded. he's quite below average when unupped, ok, but I wouldn't buff it unless I'm nerfing the upped version, and I'd rather keep it as it is. and by no means is abomination stronger than it, look at its cost.
not to mention that water already has great creature control to avoid being harassed and strong sinergies with a lot of colors.
and in my opinion, when you say "basic creatures" and mention toadfish, immortal, phoenix and charger you're stretching. they're not basic, they're the expensive, higher-than-basic cards of their quantum (as is anubis).