Save and reload before grabbing Sigil Stones. The effect is randomized each time so you can save scum to get what you want. With enough enchantments you can create builds such as: -100% chameleon so nothing can see you -100% magic resist so you're immune to spells (Absurd if you do this before joining the mage guild) -absurd speed so you can…
My first play through was completely fucked. I went with a stealth build and spent far too long pilfering people's houses. By the time I reached level 4, every enemy just completely outclassed me because I had like no combat skills. Quit soon after and created a custom build with skills I hardly used as my majors so I could better control leveling…
With any build it's trivially easy to completely break the game with spell creation. For example you can make a spell that you can cast on a shopkeeper that gives you max charm and mercantile for 1 second so you can sell junk for ridiculous amounts of money and invest in every shop, completely breaking the economy.