When looking at all currently available SARMS, YK-11 is certainly the wild card in the pack, -an exciting compound that is almost a hybrid of a SARM and one of the more potent prohormones/prosteroids of recent years.
As opposed to Ostarine and RAD-140, YK-11 is a steroidal SARM,  due to its specific chemical structure, -it binds to the Androgen Receptor (AR) and exhibits tissue selective anabolic activity (muscle and bone), but it has only a partial agonistic effect on the AR when compared to DHT; technically, any compound that selectively activates the AR can be classified as a SARM, -even if it does blatantly belong to another category of hormones entirely (as YK-11 appears to).
But this is where the comparison to DHT ends, and to all other androgens for that matter, because YK-11 exerts its unique and powerful anabolic effects through a combination of AR activation and induction of supraphysiological levels of follistatin expression.
By increasing follistatin expression, YK-11 indirectly inhibits myostatin and facilitates anabolic effects in the body far greater than would be possible otherwise.
Here it is worth noting that mice that lack the myostatin gene have double the muscle of regular mice; mice that have the same gene mutation but also overproduce follistatin simultaneously have approximately four times as much muscle mass as normal mice.
Even though this compound is still relatively new and largely misunderstood, impressive gains in muscle size and strength accompanied by improved body composition are routine with stand-alone use, it likely still holds a lot of promise. As a partial agonist of the AR, it also lends itself well to being stacked with other SARMS or whatever else you choose, with a half life of around 12 hours, the post-workout window looks best.
Rapid gains in lean muscle mass
Good strength gains
Potent myostatin inhibitor
Bodyfat loss and muscle preservation
Significantly Decreased estrogen