At the end of every trial in Hell, the party gains a Tear of Bhaal, which is needed to progress and it gives Gorion's Ward a bonus, depending on the outcome of the trial. IN total the player character gains 5 tears of Bhaal. A good or neutral character taking the evil path in any of the Hell Trials will have their alignment changed to Neutral Evil. In BG2:EE character's alignment is changed to corresponding Evil (e.g. Chaotic Neutral will become Chaotic Evil) and this will also cause paladin and rangers to become Fallen, losing their class benefits forever.
Test of Fear Edit
Good: Immunity to +1 weapons or less
Evil: +2 CON, Nymph Cloak
Exploit: ask time to think from the demon, then get the tear, gain the reward, then come back and ask the Nymph Cloak from the demon.
Test of SelfishnessEdit
Good: +10 magic resistance, -1 DEX, -2hp, -75000xp
Evil: +2AC, party member taken (if any) is permanently killed
Exploit #1: if you have a partymember make it hasted (might also need Spell Trigger: Dispel), and let it open the doors from the inside. This at least prevents the loss of DEX (but not the -2 hp), or the death of the character as punishment.
Exploit #2: before opening the good doors cast Spell Immunity: Divination. You won't loose anything.
Exploit #3: right when the conversation ends with the demon pause, and talk to it again before it teleports to the other side. Now you don't have to open the doors. If you want to go in for the healing potions, use the evil doors, as there won't be anyone to die. You get the good reward for this.
NOTE: the evil -2 AC bonus only works until your character reaches the AC-limit of -20. If it goes beyond -20, this bonus will be lost.
Test of Greed Edit
Good: +2 to all saving throws
Evil: +15hp, Blackrazor +3 longsword
NOTE: In BG2 it is possible to pickpocket the good tear from the genie, thereby getting both the good reward and Blackrazor. This is not possible in BG2:EE
Test of PrideEdit
Good: +20% fire/cold/electric resistance
Evil: 200000 experience, Time Stop Scroll, Wail of the Banshee Scroll, Sphere of Chaos Scroll, 20 bolts of lightning, 20 arrows of acid, ring of protection +2, robe of the evil archmage
Exploit: not a big thing, but if you say you won't kill the dragon, you can do it either way for 22,000 exp and still get the good reward. The beast won't have any of the scrolls though.
Test of Wrath Edit
The Bhaalspawn summons Wraith Sarevok, the ghost of your brother (confirmed in Throne of Bhaal not to have been an illusion), who goads you into accepting the powers of Bhaal and transforming into the slayer.
Good: +1 WIS, +1 CHA
NOTE: In BG2, you also receive +1 to your class's primary stat due to a bug. This is removed in BG2:EE.
NOTE ON NOTE: the +1 class-stat wasn't a bug. It only happened via a very specific route of conversation, so it was an easter egg bonus.