Hey =) Can someone help me to find a good battle set? I have a tier 4 battle pet. I have the weapon "forest blade" if its important to know. Is the forest blade a permanent weapon, or will it disappear if i use it once? I would like to defeat the carrot as well! Thank you!

The carrot should be extremely easy for you. The forest blade is infinite. You could probably just pair it with an UltimaPlus Tag and slice through him in one hit. I've been killing him on my tier 3s with just an ice bow and replica minotaur knocker.
There's a thread for set advice by tier here: https://subeta.net/forums.php/read/6318/Weapon-Advice-By-Your-Tier
I wouldn't invest too much into anything in that tier unless it scales. T5 is when you start getting into some fun toys.
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for t4, I'd just use two as attackers, they're pretty decent. should get you through the carrot with no problem.
that guide linked is pretty good, it depends how much you want to spend on stuff and how dedicated to battling you want to be. you should also look into raising your int if you haven't yet and invest in some scrolls.
forest blade is infinite use so you don't need to worry about it disappearing.
Hey battle =) thank you for replying, i managed to defeat the carrot, thanks =) I looked at the thread and i think i will save up sp for better weapons =)
thank you for replying and your explanation for the weapon =) i hope i can battle harder enemies soon too =) but could i ask which scrolls you mean?

Divine denizhen is probably a good one to make right now. Perilous whirlpools can be handy for some defense and freeze chances, but it depends how much AP you currently have. It's important to read as much as you can and raise your int so you can equip more scrolls :)