Olwen is, upon join, instantly your best healer. He can use every single healing Orb in the game, and joins with a lot of rare ones that can't be taken off of him.
He is also the only healer in the game that can use offensive magic outside of the incredibly rare Holy magic weapons. This is not, however, that useful since he has 1 base weapon skill in all of these magic types and a 5% growth in each, and, although you can raise his accuracy with bands and authority bonuses, he won't typically be fighting much. His role is as a healer, and he does this job better than anyone else.
Olwen does have one thing that offsets him, however. He, on turn 20, turns into a Raze Priest with an S rank durability Janura - this can be a massive headache for the player if he ends up transforming. However, he can simply use the Return skill to warp off of the map on demand, more or less nullifying this gimmick completely. It also provides him an additional niche in that he's the one healer that is good in escape maps: other healers take ages to traverse the distance to the escape point because of their poor 3 movement, but Olwen can simply warp away.
Upon his permanent recruitment, he can transform into a Raze Priest at will without losing control, allowing him to use the very handy Dark Heal and Janura. These provide him with additional helpful utility.
Overall, so long as you're relatively quick, you won't have trouble with Olwen's gimmick, and his pros as a staffbot and utility unit definitely outweigh his only real con.
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