Blue
Ravenous Bugblatter Beast of Traal
That raises the separate issue: Why haven't you seen the obvious decisions being made in your 13A game? Are the character somehow not aware of how their powers work, and what it takes to recover? Or are the players meta-gaming by not seeking out easy encounters, the way that their characters would if the world actually worked that way?
The way I see it, the options are continue what they are doing and have another encounter, or derail what they are doing and hope that they can find an encounter nearby and hope that it's easier then the encounter they wanted to do next. That's a lot of uncertainty.
It seems a no-brainer that it's in the party's favor not to search for the extra encounter. It derails what they are doing, it doesn't promise to be easier then just continuing on, and it adds in another chance at death overall - 8 encounters are easier then 8+1 more encounters. It doesn't grant XP because the levelling system doesn't work that way.
Oh, and the Dm can make it less than 4 for harder encounters or more than 4 for easier, so a cakewalk may not reset everything.
I guess that IF they knew what they wanted to do next was going to be really tough AND they just happen to have already had exactly 3 encounters they might search for another. Quite the corner case.