1) He's the youngest rat.
2) He doesn't like to be forced to do things, but he doesn't like to disappoint authorities so he usually does as told.
3) He likes to make references to things he enjoys but gets a bit sad when people don't get it.
4) Prefers to ignore his issues and joke.
5) He trusts Shelby more than anyone else, but respects Apo and Owen the most.
6) He knows who Tommy is, but since Tommy isn't part of the rat smp, he can't see him.
7) Being the youngest rat, he craves to defy authority more, but he can't take being disciplined for his actions, so if he sticks to any adult rat, he usually clings to Apo.
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BONUS HEADCANONS!
1) Tubbo has some form of mental issue which causes him to lash out over small things (like when he tries to kill Scott), so a lot of the other rats don't trust him too much anymore, this causes him to isolate himself quite a bit, barely being able to trust Shelby anymore in fear that she might fear him too.
2) Tubbo usually hides in the tunnels or in small spaces whenever he thinks things are too much like if he thinks people are starting to "gang up" on him even if they aren't, he'll run off into the tunnels or a small space to try calm himself down, usually it doesn't work so either Apo, Owen or Shelby have to help him calm down.
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That's all I've got for now! Hope you have a nice day!