I don't really understand usage of shroud here. I would have expected this to be some sort of a drawback enchantment given that keyword but rather it even has a self-sac ability to get rid of it supposing it were targeted by removal (given you have the mana up, but still).

Seems to me the design would just be cleaner if it didn't have shroud.

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If by "a modern set" you mean the digital-only 'Masters Edition IV', I think that's a bit of a stretch considering it only consists of super retro cards from like 1994.

Even Water Elemental itself was uncommon in a modern set. I have no reason to touch that particular thing right here.

With more than 4 power in blue at common without a drawback? Those are quite numerous - almost expected these days.

Some examples: Beluna's Gatekeeper, Brine Giant, Cryptic Serpent, Daggermaw Megalodon, Dreadlight Monstrosity, Gearseeker Serpent, Kiora's Dambreaker, Marauding Brinefang, Scrapdiver Serpent, Striped Riverwinder, Spined Megalodon, Tidal Terror, Tolarian Terror, ...

Maybe your memory banks on this haven't been updated for a while? Or perhaps you misthought this particular question (like forgetting to include some sort of a mana value clause). Regardless, these big bois started appearing around 2016 in blue, seemingly becoming quite commonplace at 2020+ era.

For your defence, those sort of designs tend to cost 6+ although do quite often have some sort of cost reduction or alternative mode (cycling, adventure, etc) or self-protection / evasion (hexproof/ward and gaining unblockability) that would naturally push their base cost toward those higher mana values - as in implying that their efficiency would and be in-line at that rate to technically allow a design like this Water Elemental. Regardless, having one simply at mana value of 5 would be unprecedented to my knowledge. It's sort of a grey space, where I think that sort of design is avoided for blue's identity as the color with the weakest 'raw stats'-to-mana ratio and preference to avoid pure stat monsters.

I briefly considered white/blue hybrid. Blue does have Clerics, so it is open whether Aerie Worshippers have a blue-aligned concept of holiness.

Have you ever seen a blue common creature at that mana value with power greater than 4 without drawback?

Idk, seems like bit of a hard sell to somehow not have this as a white creature. It's not like blue is that into 'irrational' concepts such as 'holy'. Generally 'holy water' is just water that has been blessed by a priest though maybe for whatever setting this is for that wouldn't be the case.

Why isn't this a common?

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