Looking at a Random Card: Dimir House Guard
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Dimir House Guard: To discuss this card, you have to discuss the transmute mechanic. WotC realized from the beginning that Transmute had issues, enabling very focussed decks bent on repetitive play, especially combo decks. That didn’t stop them from printing cards with transmute, though, but they did this obviously very conscious of those cards’ power level, which led to transmute cards having a seemingly random variance of different, often obscure abilities besides transmute. There were a number of cards which were practically useless unless transmuted (e.g., Dimir Machinations and Ethereal Usher) – the worst possible solution to the issues WotC was concerned about, in my opinion, since it reduced those cards to the very tutoring function which created those issues. There were a few cards which would have had marginal play value in constructed without transmute, and thus succeeded in sometimes actually being used for their seeming main purpose, but even those were usually included in decks with the main intent of using them as a tutor (Tolaria West, Muddle the Mixture, Drift of Phantasm). One card was almost always played in limited, but almost never transmuted there (Brainspoil), and there were a couple of cards which were useful in limited when played, but were also transmuted a good number of times. Dimir House Guard falls into that camp.
This creature’s abilities are possibly best described as “hodgepodge”: You get a marginally useful evasion creature with a somehow random regeneration effect, which requires you to sacrifice a creature, tacked on. (Of course, this regeneration ability is a forced tie-in with the mechanics of the Golgari, and to a lesser extent, Orzhov – Ravnica block needed a lot of cross-synergy between guilds to work in limited.) Both the evasion and the regeneration ability are slightly underwhelming on a 2/3 for 4 mana, but in combination, they were enough of an incentive to put this creature on the battlefield in many situations. Of course, in the comparably slow Ravnica limited environment, it was always tempting to exchange the Guard with one of your other 4-mana cards, since chances were good you’d be able to find something better.
From a constructed perspective, the 4-mana transmuters were maybe especially problematic, since 4 mana is typically the slot holding those cards defensively-minded decks use to take control of the game (Wrath of God, Fact or Fiction and Flametongue Kavu are examples of such cards), but also because you will normally tutor up the card you want to play on your very next turn, with the cost of 4 mana being the natural follow-up to the transmute cost of 3. Thus I don’t think it is coincidence that mono-Blue didn’t get a 4-mana transmuter – this powerful ability probably seemed a bit safer in decks requiring black.
I believe it were considerations like these leading to the disjointed and inelegant feel of this card. For constructed reasons, it is a miss in my book, since it would only get played in decks which ideally shouldn’t exist – I can see Drift of Phantasms, for example, in some kind of interesting “tool-box”-deck adapting to its opponent’s strategy, but the Guard will inevitably lead to a narrow deck design looking for repetitive play. For limited environments, however, this card is actually not that bad a choice – although designed specifically with the requirements of Ravnica block in mind, it is generically useful enough that it could help out in many different environments in need of a multifaceted card. Still, I don’t like it much, because it is just not a feel-good card: You’d never really want to play it for any of its three main functions (evasion, regeneration, transmute) by itself – it is always a compromise between three subpar options hoping that one of those will turn out satisfying in the context of a specific game. While this is an acceptable concept, I prefer a different execution of it: The charms from Mirage, Visions, Onslaught and Planar Chaos are more to my taste (not every one of them, of course). I feel a 4-mana creature should play a defined role in your deck which you can rely on and not be a filler with fluctuant value. Flimsy effects on cheaper cards are fine, but 4 mana is enough that you should know what you pay for.
So, for me Dimir House Guard is a constructed flop with a slight tendency to encourage unpleasant decks, and a useful, but unexciting limited tool not to my taste. There’s not much to say about its flavor either way. I give it a D – or, more precise, a D-, because of its possible undesirable effect on a constructed environment.