I'd say that both version of the feral Tieflings can be really good rogues/assassins. ... So, yeah, Feral Tieflings is definitely a very good race for an assassin, not only for the +2 Dex, but also for the other race features and the +1 Int, which always help with Investigation.
two horns
To this specifically, there are no mechanical features of the Tiefling tied to their tail--it's purely cosmetic. So there will be no change to gameplay on account of a player deciding their Tiefling doesn't have a tail.
traditionally, tieflings have some semblance of horns and tail but that doesnt mean they all keep them. ... Most of the devils in the monster manual doesn't have both horns and tail.
The vast majority have feet. But it's not unheard of. By default, there is no mention of hooves in the PHB. But there's appearance-options for cloven feet in the SCAG.
The phb says human or shades of red skin, but if you take a look at SCAG (sword coast adventure guide) there's a sub race of tiefling called feral tieflings. In their description, they can have blue skin.
150 years
As you can see from above, Elves can have babies, and they reproduce the same way as Men do, but they usually do it when they are young, Elvish libido diminishes over time, and having children is exhausting for Elves.
New Christmas elves and other kinds of elves are born frequently. When the last rays of the evening sun meet with the Northern Lights, the wind is from the North and the stars are shining, that's when elves are born.
mortal biology, Tolkien said that “Elves and Men are evidently in biological terms one race, or they could not breed and produce fertile offspring." ... So, long story short, I'm pretty confident that elves do menstruate.
[edit] Sexuality, marriage, and parenthood. Elves marry for love, or at least with free will from both parties, typically early in life. ... They marry only once for it was ruled by Manwë that, "'since the Elves are by nature permanent in life within Arda, so also is their unmarred marriage.
Elven Kingdoms
TL;DR: Thorin is half-elf, and Fili and Kili are themselves both part elf and half-human. The two young dwarves represent the union of Elves, Men, and Dwarves that once existed before Dale fell, and which will rise again.
Fíli and Kíli were nephews of Thorin, who was the elder brother of their mother Dís. They were also nephews of Frerin, grandsons of Thráin II, and great-grandsons of Thrór. Fíli's most distinguishing feature was his long nose, the longest of any of the Dwarves in Thorin's company.
Dain
Tauriel admits her love for Kili in The Hobbit: The Battle of the Five Armies. ... She successfully finds Kíli and the two battle against Bolg together. She is overpowered and almost killed by Bolg, but Kíli sacrifices himself to save her.