Ho there, adventurers!

I'm going to replay the whole saga with a Mage in a Good aligned party.
In BG the thieving should pose no problem, having Imoen in the party since the beginning but I'm not quite sure about BG2. Coming out of Irenicus dungeon I could use Yoshimo until I reach Spellhold and then take Imoen back with me, giving her the dead Bounty Hunter's equipment.

The question is: are Imoen's thieving skills, even with magic items' bonuses, enough to get me through ToB? The other choice could be Nalia but she's an even lower level.

Thanks in advance and, please, gather that damn party before venturing forth.

I believe that, with judicious use of spells (like a Cleric's FInd Traps), potions and stat-boosting items/magic, it is indeed possible to get through ToB using only Imoen's thieving skills. Naturally though, it means you won't really have access to Thief HLA's (traps, in particular, can make many difficult encounters WAY easier). If you're on PC you could always try using EEKeeper or similar programs to hack Imoen back into a pure-class Thief; that's what I wound up doing when I played through the game as a Mage myself.

What is this EEKeeper? Is it some kind of hacking software? I'm not very handy with such things.

I guess that I'm trying with Imoen and plenty of stats boosting items. If it is not enough I'm gonna have to dump her for Jan Jansen (no other Thieves are available).

first of all yes keeper is a hacking software, and if you are playing EE then Hexxat is a great thief but she sucks blood so I assume that leaves her out.

Sarevok is my best Tob thief... again not the best choice for goodie two shoes

now what is a thief;
set traps, backstabs, scouting, open locks and disarm traps

Imoen can do the scouting, open the locks and might be able to backstab but the damage she does won't matter [many bosses in tob are immune]... she can't lay traps for shit but you can take a Blade character to handle traps

disarming traps is possible for her but its not something she does well

Well, I'm going to leave scouting/exploring to either Valygar or Minsc: Rangers just do it better.

I'm only going to use Imoen to find/disarm traps and open locks.
By the way, you said that Imoen can open locks fairly well but she's not very apt at disarming traps.
Aren't both actions based on the same skill?

She will be perfect for this job through ToB.

I said Disarm Traps.

Detecting traps and disarming traps rely on the same skill, 'Find Traps'. Though, each trap has separate "detection difficulty" and "removal difficulty", with the latter usually being higher. You may be able to detect a trap but not able to remove it.

The thing is imoen is a mage that can wear thief items not a thief that cast spells... Enjoy your game

Now I get it! Thanks!

As previously posted, Thief magic items will enhance Imoen's Find/Remove Traps and Open Locks skills to be good enough for the whole BG Saga. She acted as my Thief the whole way (except when with Yoshimo), and I don't remember having issues with locks or traps.

For locks, I do remember having Imoen always memorize a 2nd level Knock wizard spell, just in case I came across a lock that Imoen's skill was too low for. I don't remember how much I had to use Knock, but I don't remember it being too often. And there were also Potions of Master Thievery that would temporarily raise her Open Locks skill, something like +40%, but I always hoarded my potions and never used those.

For traps, I do remember having Jaheira memorize a 2nd level "Find Traps" priest spell for a while. It doesn't "Remove Traps", but it's serviceable because after detecting a trap, usually my six munchkins can just walk around and avoid the trap. But I eventually stopped having that spell take up a slot for Jaheira, as it's hard to know when to use it. (I try to play as though my peeps don't know exactly what's down the hall, even though I do.)

The real downside of having Imoen wear Thief magic items, is that she's not wearing Mage magic items. But I had Aerie in my party, so the Mage stuff never went to waste. BG2 is better suited for more than one Mage in a party of six anyways imho.