Swithing power and toughness isn’t something that happens a lot in Magic. Usually, because it’s hard to find cards where it’s interesting. Of course, there have been cases in which it was done simply for the sake of doing it, but it was quickly found out those cards didn’t do much for the game as they are quite situational, so the newer iterations were either pushed or R&D tried to do something more interesting with them.
As it so often happens, the earliest examples are in a different part of the color pie than the latter ones. The earliest example of switching power and toughness came in Legends (1994) in the form of [scryfall]Transmutation[/scryfall], a black card.
These cards don’t get reprinted often, but for some reason, this was seen as important enough to be printed also in Chronicles (1995). Well, Chronicles was a huge mess in many respects.
The next iteration on the idea was from Alliances (1996), where the [scryfall]Phantasmal Fiend[/scryfall] was still black, but the cost for the activation for switching was blue, so essentially while the card was black, the ability was blue, so the effect had already changed colors.
Next year (Weatherlight 1997) the ability was moved to red, where it stayed for quite a bit.
[scryfall]About Face[/scryfall] from Urza’s Legacy (1999) was simply a color-shifted [scryfall]Transmutation[/scryfall] further signifying the change in the color pie.
Torment (2002) shifted the ability to blue, which is where it has largely remained since then. As more experienced players know, the ability to discard for free can be very strong ability, so this is has seen some play. It was even used in Vintage Masters.
In Fifth Dawn (2004), five years after the previous example, a colorless card received this ability, although with quite a high activation cost (and the creature itself is quite expensive for what it does as well).
Later that same year, in Champions of Kamigawa (2004), we had this little gem of complete unusability. Paying 2R for this effect, even in the highly over-costed block of Kamigawa, just doesn’t really cut it. Splicing might be nice at times, but using it as a trick that way seems awkward.
Mannichi from Betrayers of Kamigawa (2005) wasn’t quite the last monored card to do this, but red mostly lost the ability, even though it seems to have become a common theme for blue-red creatures. Mannichi has a weird effect, because it switches it for everyone, instead of just target creature. Hard to see much use for it, except that perhaps you can force bad blocks in some cases.
[scryfall]Windreaver[/scryfall] is a strangely overcosted rare from Dissension (2006). The card was printed again later as a part of a Venser duel deck.
This is a weird card. Maybe a little overcosted, but not necessarily. Again, not much use as usual, but on the other hand, it was reprinted in Conspiracy (2014), where it found some use in a multiplayer environment, where there are more potential places to use the ability.
This was a direct color-shifted callback to [scryfall]Dwarven Thaumaturgist[/scryfall], which was a common theme for Planar Chaos (2007).
Because turtles historically have a low power and high toughness, the switching ability suits them pretty well. It’s also flavorful, because in reality, turtles are often well protected in their own environment, but sometimes have to come out of it for certain things.
Next year in Eventide (2008), we got [scryfall]Inside Out[/scryfall], which is now between red and blue, which was a common theme for the set. Here, the card is worth only one mana, when compared to previous versions of this card, so we can see that the ability is now valued lower than before.
[scryfall]Crag Puca[/scryfall] on the other was hard to cast, but efficient at 2/4 for three mana. The ability cost one more mana, but made this a fairly efficient attacker, as it makes combat math quite a bit more difficult.
The precedent was set by the [scryfall]Turtleshell Changeling[/scryfall], so apparently this is now a turtle thing, and again, it does match the flavor. Because it’s Worldwake (2010) and set in Zendikar, we have a Landfall ability. The Shroud makes this somewhat less usable, though.
This thing from Rise of the Eldrazi (2010) is an interesting card, but probably not very usable. It does make attacking quite awkward for the opponent, because they have to leave blockers back, because this can hit really hard, even if it dies quite easily.
Year 2010 was apparently quite big for this mechanic, as this is the third card printed in that time. For some time, this was the premier example of this mechanic, as this card saw some play in various Infect decks in Modern as an answer to [scryfall]Spellskite[/scryfall]. It might see even more play now, as some people have been advocating moving the traditional GW approach to Bogles into UW, but I’m not sure that will catch on. We can see here that compared to certain other cards of this type, they’ve again re-evaluated the actual worth of this mechanic and brought the cost down again by giving the card draw with now extra cost. Since it’s finally seeing fringe play, this was clearly the right way to go.
It took a few years for us to see the next example of this mechanic, but Dragon’s Maze (2013) finally brought this creature, which combined the caring about spells (a theme which has been pushed quite hard in recent years) red-blue already has with switching. This space has probably now been pretty much scoured, though.
The final entry thusfar. Oath of the Gatewatch (2016) filled out the 10 card cycle of two-colored creature-lands. White-black had lifelink, blue-green had hexproof, black-green had deathtouch and red-white had double strike. What could blue-red have? Giving it prowess wouldn’t really sit well, because that would require quite a bit of mana to be usable in any way, so it got switching.
All in All
There’s only 19 cards here, so there isn’t a lot of room for this ability. It’s way too situational to be useful and it also has quite a bit of rules baggage, so it should be used sparingly.
Usually these creatures will have low power and high toughness to make using them worthwhile and give the creature more flexibility. Switching the power and toughness on a 3/3 isn’t going to be very interesting, but doing that to a 1/4 makes an unassuming creature an actual threat.
It is interesting that there’s only one of these creatures that has a higher power than toughness ([scryfall]Crookclaw Transmuter[/scryfall]). Why is that? It probably produces less feelbad moments, as the creatures are less vulnerable to various things this way and it’s harder to get caught off-guard.