My Top 5 most useless would have to be:
1. Meg - On Normal she was useful in one mission as a meat sheild one a couple levels but on Hard she is the first one to be left sitting on the bench when selecting characters.
2. Vika - This ones not entirely fair because I havnt given her a fair chance in either play through. By the time I tried her out it was to late in the game and I had neglected her to long. I dunno if she has potential or not.
3. Heather - Similar to Vika. Never got her chance to shine. Plus Soothe and Volke are just so kickass why would you bother??
4. Leonardo - He's just such a wuss. The other archers can each hold their own and take a few hits. This guy just needed waaaay to much babysitting to get anywhere. Hes like the male version of Meg in my opinion.
5. Laura - She just kind of fails as anything other than a healer. Both Micaiah and Mist can be freaking amazing at endgame with some attention but Laura just isnt good for anything other than getting Aran to join.
The only reason I left Fiona off the list is because shes mounted. I've used her several times to trade items between characters and run away or rescue allies and run away. I've never put a single EXP point into her but shes still been strangely useful on the battle field as a gopher.
EDIT: All the Laguz suck with the exceptions of Volug (only early on) and the bird tribes. This includes Dragons.







