List of things that available in this post:

1. Lost Worlds

2. Make money fast (with some mathematical circumstances)

3. Glitch Ticket

4. Vanity Badges

5. (NEW) Partners

First, about Lost Worlds:

Lost Worlds is actually the old Master Quest, but since it's replaced by story quests, it will not continued anymore.

Instead, it will be a secret rooms, called "Lost Worlds".

There are 3 Lost World, and here is a photo for the hints.

Lost World 1:

In Toriel's room, go to the right. Hint is on the book.

Lost World 2:

In Sans' room, same like the place of the Bad Tom fight.
Bad Tom is also in there. Hint is on the Sans' table.

Lost World 3:

In the halfway of the Core, go to the right. Hint is on the room where the Royal Scientist works.

How to make money fast (in my own way)

Preparation:
Charm with C Level.

First, fight Bad Tom. When you fight him, make sure to put Charm (C) on him. Then, kill him. You will got 546 G.
Revive him only costs 45 Undercoins (450 G).
So, you will get a bonus 96 G.
Fight him again, and do the same.

Glitch Tickets:
The only obtainable thing, that can be taken from daily rewards in Online. When you play offline, there's no daily rewards, making it impossible to get it. This can be used to summon corruption battles, which more easier to get.
You can summon it by giving the Clam Follower the tickets.

In V2.5.0, they are costs 5 glitch tickets.
In V2.5.1, they are costs 3 glitch tickets.
In V2.5.2, they are costs 1 glitch ticket.

See? @RickyG was really kind, he decreased the amount of it, just to make us getting corruption battles more easier to get.

Talking about daily reward, it can contain one of the following rewards below:

1. Gold (G)

2. Undercoins (UC)

3. Pogs

4. Glitch Tickets

And, vanity badges.

It gives signs of how much you keep progressing.

For genociders, you will be granted with knives symbol.

For LV 20+, you will get bronze knives.
For LV 50+, you will get gold knives.
For LV 99, you will get diamond knives.

And for pacifists, you will be granted with save symbol.

Same like before, but with save symbol.

There are also badges for admin only, that looks like a soul.

Same, same, same. Bronze, gold, diamond.

However, you can use command /togglebadge to show your badge, or even hide them

And lastly, partners.

They can help you with increasing your ATK in some attacks, DEF, increasing EXP or GOLD in every battles, and much more!

If you use a vessel that have a bond as seen in Undertale, Deltarune, or whatever, it will gives another bonus as well!

Example:
Partner: Mettaton.
Stats: Increasing EXP.

By using Napstablook vessel, it increasing your EXP more, and also increasing your GOLD as well!

You can get partners throughout by corruption battles.
Corruption battles can be happened after a fight with a monster, but very rare. You also can spend Glitch Tickets for the battles, too! If you want to know more about Glitch Tickets, see above.

Well, that's it. Have fun!