So Quick point to make this bug is useless on pretty much any category that doesn't require a fresh account. Regardless I did find it, it seems undocumented and actually Speedrun viable only problem is its lag based. I don't know if lag based bugs would even be allowed in speedruns so I'm curious.

Way the bug works: You can buy tower upgrades you don't have the EXP for (potentially even ones you dont have the money for)

Explanation: I was doing a coop Bloons stream and the players around me had horrible ping as the game would constantly pause or revert however because of this I somehow managed to buy an upgrade I didn't and still don't have unlocked due to lack of exp with only one other player in the coop game. Time stamp for the bug starting is 2:56:30 and this is my stream vod here. Its the T4 alchemist I bought if you keep watching you will even see that I notice the bug during the game.

I cannot answer this question fully, as of course I am not a moderator, but I think that this bug would not be allowed. Also, there are only a couple category extensions that use this that are never played so this bug doesn't matter to 99% of runs.

Ty for bringing this bug to our attention! There's a general statement in the rules that any bugs are not allowed in runs, this would fall under that. But it's good that the team is now aware of this so we can spot it. Thanks again!