What fiend summoning spells do wizards get at 3rd spell level?
Or are these Xanathar spells? I don't have that book, so, I have no idea.
Yeah, they're XGtE spells.
At 3rd level, you get
summon lesser demons, which calls in a bunch of low-grade demons - manes, quasits, that sort of thing - and drops them on your enemies' heads. You don't control the demons, they just attack anything that moves. They vanish as soon as you stop concentrating, and you can make a warding circle that protects a single creature of your size or smaller. However, the warding circle requires the blood of a humanoid slain within the last 24 hours*.
At 4th level, you get
summon greater demon and
infernal calling, both of which summon a single more powerful fiend and give you a measure of control... shaky, dangerous control. You can hang onto the summoned creature as long as you dare. It keeps getting saving throws to break loose. If you stop concentrating, it vanishes; but if it's broken free, it gets a little extra time to nosh on you before going back. Again, you can do a warding circle for protection, if you don't mind murdering someone to get the component.
They're very thematic and flavorful. If you want to play a fiend summoner, XGtE has you covered. If you prefer to play with less malevolent forces, however, you're out of luck. Personally, I see no problem with limiting wizard summons to fiends and elementals; I just wish there were more options for elementals at lower levels.
[SIZE=-2]*The blood is a material component for all of these spells. There's no listed cost on the blood, so normally you could use an arcane focus instead. However, the description of the warding circle is quite specific that you draw it with the blood used as a material component. So, the way I read it, you can cast the spell with an arcane focus and no blood, but then you can't have a warding circle. This is definitely up to DM interpretation though.[/SIZE]