Unlockable Trial Mode Characters
Characters usable for trial mode.

Oliver - Clear game 3 times.
Shiharam - Clear game 5 times.
Petrine - Clear game 7 times.
Bryce - Clear game 10 times.
Ashnard - Clear game 15 times.

Unlockable Connect-O-matic
You can unlock crap if you connect your Gameboy Fire Emblem with your Cube Fire Emblem.

Fire Emblem illustration.
The Sacred Stones illustration.
Trial map 4, Fire Emblem or Sacred Stones.
Trial map 5, Fire Emblem.
Trial map 6, Sacred Stones.

Hint: Reset Code
If things aren’t going your way in a mission and one of your characters dies, it’s advisable that you retry the level. Like many GameCube games, Fire Emblem: Path of Radiance features an undocumented reset function. Simple press and hold X, B and Start and the game will reset to the title screen.

Hint: Better Stats
Once you are able to upgrade character units in-between missions, be sure to carefully watch how many stats point upgrades your character receives every time you pass the 100-point mark. Since Fire Emblem randomizes the upgrades, make sure you maximize your character stats upgrades by resetting the game and reloading from your last save point if no or few point upgrades are given during level-up. To this end, make sure you save your game after missions and every time one of your characters receives a satisfactory bonus.

Hint: Class Change Effectiveness
When you have the option of changing a character's class, don't evolve the character at level 10, because the person you are evolving will not have gained the same benefits as a person evolved at level 11 to level 20. So, at least try to evolve them at level 15, but if you want an incredibly strong character, evolve it at level 20.

Hint: Train A Healer
When you are in a battle where the only person left is an unmoving boss, and many of your units are injured, don't use vulneraries, forts, or any other healing item. Instead, use a cleric, monk, bishop, or valkyrie's staff to heal those characters. This will gain experience for the healer and mend injured players for the battle against the boss.

Hint: Easy Boss Kills
If the boss does not move, and only has an inderect or direct weapon, there is an easy way of defeating it: Simply attack with a direct weapon if the boss has an indirect weapon (bows, not any type of magic), and attack with an indirect weapon if the boss has a direct weapon. Try to use a character that you want to level up, though.

Hint: Recruit Nasir
You must defeat the Black Knight in chapter 27 going on to 28. You fight him and Mist comes with Ike, but she needs to be promoted by this point, or you'll have a difficult time. Mist has to be able to kill the healers (Bishops) and the one soldier that appear to assist the Black Knight. You must be able to defeat the Black Knight in five turns or less or else Nasir will not be available for the rest of the game.

Ike should ideally be at level 20 or more. Have Mist promoted by at least by one level. Have Mist occupy the Black Knight's flunkies and focus your heaviest hitters on the Black Knight. Good luck.