user375: The FEN is:
r2qk1r1/ppp2p1p/2n1bn1Q/4p1B1/8/2P4P/PP1NpKP1/R5NR b kq - 0 1


Clearly black is winning because the white bishop can be captured (with a discovery available if white recaptures). However, the stockfish eval seems strange - why would it suggest that playing an intermediate Rg6 is better? The continuation is Qh4 Rxg5 Qxg5 anyway, which is just a slower way to do the same thing. Wouldn't it be better to play the most direct move Rxg5?
Then I am also confused about the 3rd recommendation of e1=B+, why would it suggest to underpromote there?

user924: I think that in the case of the immediate ...Rxg5, Stockfish has seen one move deeper than in the version with ...Rg6 first. As a result the evaluation is slightly different - 0.1 less, in this case. So it ranks ...Rg6 first. It doesn't really matter either way, it's just an artifact of how engines work.
Same for ...e1=B+. It gets captured immediately, so it's effectively the same move as ...e1=Q+ that would also be captured immediately. Which one it happens to show is essentially random, it doesn't have a builtin preference for promoting to a queen in cases where it doesn't matter at all.

user825: No particular reason. Note the scores, -8.9 and -8.8, practically indistinguishable. Stockfish simply saw the same sequence of tactical response with and without the move ...Rg6. The line ...Rg6 came first due to random fluctuation.

375: <p>The FEN is:</p>
<pre><code>r2qk1r1/ppp2p1p/2n1bn1Q/4p1B1/8/2P4P/PP1NpKP1/R5NR b kq - 0 1
</code></pre>
<p><img src="https://i.stack.imgur.com/hJjNV.jpg" alt="engine" /></p>
<p>Clearly black is winning because the white bishop can be captured (with a discovery available if white recaptures). However, the stockfish eval seems strange - why would it suggest that playing an intermediate Rg6 is better? The continuation is Qh4 Rxg5 Qxg5 anyway, which is just a slower way to do the same thing. Wouldn't it be better to play the most direct move Rxg5?</p>
<p>Then I am also confused about the 3rd recommendation of e1=B+, why would it suggest to underpromote there?</p>
 924: <p>I think that in the case of the immediate ...Rxg5, Stockfish has seen one move deeper than in the version with ...Rg6 first. As a result the evaluation is slightly different - 0.1 less, in this case. So it ranks ...Rg6 first. It doesn't really matter either way, it's just an artifact of how engines work.</p>
<p>Same for ...e1=B+. It gets captured immediately, so it's effectively the same move as ...e1=Q+ that would also be captured immediately. Which one it happens to show is essentially random, it doesn't have a builtin preference for promoting to a queen in cases where it doesn't matter at all.</p>
 825: <p>No particular reason. Note the scores, <code>-8.9</code> and <code>-8.8</code>, practically indistinguishable. Stockfish simply saw the same sequence of tactical response with and without the move <code>...Rg6</code>. The line <code>...Rg6</code> came first due to random fluctuation.</p>
