My name is Jaden and I'm fairly new to editing the UESP Forum - however, I'm thoroughly enjoying the experience so far! :P I play Oblivion on the Xbox 360 Console :) Sorry about all of the spoilers found below xD
I have three main glitches which I have fallen prey to and hope that in the creation of this section, you won't fall prey either! All of these glitches are mentioned on their respective pages but I failed to notice them and so I paid the price :P
- Losing Shadowmere - I had downloaded the Horse Armour Official plug-in from the Game Marketplace and kitted Shadowmere out with this great-looking armour now available. Little did I know that when Shadowmere uses this armour, she does infact change into a different - don't worry, she keeps the same values such as speed, appearance etc. However, what she doesn't keep is the code line that instructs her to return to For Farragut when she gets knocked unconscious and you leave the area. Due to this annoying loss of code, I have now lost Shadowmere and because I do not have the Console found on the PC versions of the game, I am unable to easily find her. She's more than likely still out there in Cyrodiil, but because I have no recollection of where I left her, she may as well be well and truly lost. If you value Shadowmere, don't use armour on her!
- Unable to Enter The Thieves Guild - This is down to a glitch that happens if you open the cell gates in the Leyawiin Prisons (using either an Open Spell or Lock Picking skills) before starting The Thieves Guild Questline. Whatever you do, under no circumstances, do not open the cell gates in Leyawiin Prison! The only way of rectifying this (and thus getting the Thieves Guild achievements) is to start another character going.
- Unable to Purchase Rosethorn Hall - This is because I became imprisoned in Skingrad Castle Prison and wanted to escape. I stumbled upon the (Spoiler Alert!) candle holder on the wall when I noticed the door shape at the end of the corridor - it reminded me of the one behind the target in Battlehorn Castle's Training Room. I followed it through and ended up in the Wine Cellar beneath Castle Skingrad. Of course, not wanting him to alert the guards, I quickly dispatched the Orc (namely Shum gro-Yarug) in the Cellars, without realising the full horror I had realised! Suffice to say, I did escape from the prison, however, I also lost the ability to purchase the lovely Rosethorn Hall. This is down to the NPC who died being the one who sells you the house in the first place. I noticed this several out-game months down the line when I couldn't find the person who sells you the house - he was dead! I had no previous saves either. You should always think about whether or not killing an NPC is a good or bad idea. I'd strongly recommend searching their name into the UESP search bar and reading through their page, just to see if they're needed for anything. If they're not, feel free to kill them. If they are, then on your head be it :)