Level 25-36

By now you would be able to go to Underfell. If you need help with the Underfell Bosses click here.
If you need help with Undertale Realm Bosses click here.

Anyways a few things to remember:

1. Start grinding Asriel until you are level 30, and then start grinding Underfell bosses WITH OTHER PLAYERS THAT CAN GO TO UNDERFELL.
2. Save up G until you are level 36: Aim to acquire at least 270 000 G
3. Finally, by now you should really aim to have the Error Blaster (Drop from Error!Sans) by the time you are level 36. If anyone gets Error, get 6 Steaks and join. If you get Error and don't have food, get others, hopefully those with the Error Blaster to take the distracting and dodge.

Oh, yeah, you should also have Chara's Knife by now, if you don't then grab the G and buy it.

And all the Underfell bosses are listed below.

• Underfell Toriel Lv 25+ (From spawn, head to the Ruins and go left at fork. Keep going straight, the Training Hall and Spider Bake Sale are to the right if you need them, and round the corner and go left when it forces you to)
• Underfell Papyrus and his Pathetic Brother aka Underfell Sans Lv 27+ (Take the shortcut at the spawn to Snowdin Town, and keep going straight. Papyrus is at the end.)
• Underfell Muffet Lv 30+ (From spawn head to Spiderlands. Uf Muffet is at the end)
• Underfell Undyne Lv 32+ (From spawn head to Waterfall. Go until the red glowing area and heal left)
• Underfell Asgore Lv 36+ (From spawn, head to Hotlands and go left but at the end you will find Judgement Hall keep going till the end you will see him in Throne Room)

So there is one Training Hall in the  Ruins, same place as before, but this time there are 3 Froggits: 2 Hard ones that have 100 Hp and a Final Froggit at the end with 200 Hp. There is also a secret. Walk into the wall at the back and you will be able to fight Jerry. Behind him there is a small Jerry that has more Hp. Normal Jerry stats: 500 Hp contact damage only way of offense and drops Glamburger. Small Jerry Stats: 800 Hp only contact damage and drops Hamburger.

So that is about it, give feedback in comments and go to the links at the top if you need help!