A character may add new classes as he or she progresses in level, thus becoming a multiclass character. The class abilities from a character’s different classes combine to determine a multiclass character’s overall abilities. Multiclassing improves a character’s versatility at the expense of focus. To multiclass a character, you need only talk to a class trainer of the appropriate class when you are ready to level.
In D&D Online, there is no experience point penalty for multiclassing, but you are limited to a maximum of 3 classes.
 Class and level features
- Level: “Character level” is a character’s total number of levels. It is used to determine when feats and ability score boosts are gained.
- “Class level” is a character’s level in a particular class. For a character whose levels are all in the same class, character level and class level are the same.
- Hit Points: A character gains hit points from each class as his or her class level increases, adding the new hit points to the previous total.
- Base Attack Bonus: Add the base attack bonuses acquired for each class to get the character’s base attack bonus.
- Saving Throws: Add the base save bonuses for each class together.
- If a skill is a class skill for any of a multiclass character’s classes, then character level determines a skill’s maximum rank. (The maximum rank for a class skill is 3 + character level.)
- If a skill is not a class skill for any of a multiclass character’s classes, the maximum rank for that skill is one-half the maximum for a class skill.
- Class Feats:
- A multiclass character gets all the class feats of all his or her classes but must also suffer the consequences of the special restrictions of all his or her classes.
- In the special case of Turn Undead, both clerics and experienced paladins have the same ability. If the character’s paladin level is 4th or higher, her effective turning level is her cleric level plus her paladin level minus 3.
- In the special case of Uncanny Dodge, both experienced barbarians and experienced rogues have the same ability. When a barbarian/rogue would gain uncanny dodge a second time (for her second class), she instead gains improved uncanny dodge, if she does not already have it. Her barbarian and rogue levels stack to determine the rogue level an attacker needs to flank her.
- Purchased feats: A multiclass character gains feats based on character levels, regardless of individual class level.
- Enhancements: A multiclass character gains racial enhancements based on character levels, and class enhancements based on class level. Class enhancements that give the exact same benefit, for example rogue dex and ranger dex, cannot be taken at the same time.
- Ability Increases: A multiclass Player Character gains ability score increases based on character level, regardless of individual class level.
- Spells: The Player Character gains spells from all of his or her spellcasting classes and keeps a separate spell list for each class. If a spell’s effect is based on the class level of the caster, the player must keep track of which class’s spell list the Player Character is casting the spell from. Spell points for multiclass casters stack into one larger pool.
 Class specific notes
- Bard: A multiclass bard still incurs the normal arcane spell failure chance for arcane spells received from other classes.
- Paladin: Like a member of any other class, a paladin may be a multiclass Player Character, and contrary to PnP, multiclass paladins can get more paladin levels after multiclassing (just like any other class).
- Rogue, Barbarian: Trap Sense bonuses gained from multiple classes stack.
The following are limited in how they can multiclass due to alignment:
- Paladin: must be lawful good
- Monk: must be lawful
- Bard, Barbarian: must not be lawful
- Druid: must not be lawful good or chaotic good
 The Art of Multiclassing
Making a multi-class Player Character requires careful planning. The reasons for this are two-fold. First, certain classes are more effective in combination than others because their primary ability scores are complementary, and it’s a good idea to pick a class combination that has abilities that blend well together. Second, skill points gained for classes, class feats, and saving throws increase differently for various classes. You’ll want to take this into consideration and plan for it appropriately.
There are basic guidelines for multi-classing one’s character. There are times where breaking these guidelines are okay, but generally they will hold true from build to build. Breaking the guidelines merits a close look at the benefits gained.
First, look at the primary ability scores of each class. For example, fighters, barbarians and rangers all share strength as important ability score for their classes. Bards, paladins and sorcerers all use charisma as an important abilities score for their class feats and skills. Therefore, if you made, for example, a sorcerer/paladin multi-class, points in charisma would be more efficient.
By the same token, wisdom is not a primary ability of most fighting classes (the Monk's wisdom determines many abilities that augment some attacks, such as Stunning Fist), so a cleric and fighter combination would be less wise regarding the blend of their ability scores. This doesn’t necessarily rule out cleric/fighter multi-classes, but it is will make them less efficient than a better class combination in this regard.
Second, How much are your classes diluted by lower levels? A multi-classed cleric loses a lot of effectiveness in his turning ability in comparison to the hit dice of the undead he meets as he gains in levels. After a couple levels of multi-classing in another class, a cleric will no longer be able to turn undead, and effectively loses turning ability. However, a ranger’s bow strength ability, gained at level 1, is not diluted by multi-classing into another class.
Third, Look at the 'sweet spots' for the classes in terms of number of levels. Classes don't improve equally at each level. Bonus feats granted at certain levels and the ability to take important enhancements makes some levels better than others. For many classes, obvious sweet spots are are 6, 12 and 18 because they get a Prestige Enhancement at that level.
-A druid will get its Wild shape Feats at 2, 5, 8, 11, 13 and 17.
-A bard gets a huge improvement to his inspire courage song at level 14.
-Many classes gain a lot of their strength from their first levels. A cleric can use scrolls, a monk can add their wisdom bonus to AC and a rogue can invest points in Search, Disable Device and Use Magic Device regardless of their level.
-At level 7, a rogue gets 1d6 sneak damage and the ability to take Sneak Attack Training III as well as Haste Boost III.
-Monks and rogues get the valuable Evasion feat at level 2.
-Clerics get the ability to cast level 9 spells at level 17.
-Fighters get bonus feats at every even level.
In general, a splash (a low number of levels in a class) can already provide much of the functionality of the class.
Look at what you levels you want to get, but also look at what levels you can do without. They could be better spent as a level in your other classes.
A popular level split for melee classes is 12/6/2 because it enables the first two Prestige Enhancements in your primary class, another in your secondary class and 2 levels of rogue, monk or fighter for evasion and/or extra feats.
Fourth, Always consider if it's worth the capstone enhancement. Many classes get a huge benefit at level 20 so giving up on that 'sweet spot' has to be worth it.
Note that it is often best to take the class with the highest skill bonus as one’s first class. This is because you receive four times the number of skill points at level 1 than at other levels. So a rogue/wizard receives 32 skill points (before bonuses) if rogue is taken at character level 1, while if wizard was taken at Player Character level 1, the Player Character would receive 8 skill points (before bonuses).
See also Splash main article
As everyone knows, Rogues and Artificers are always useful as they are the only ones to disable traps. In order to gain full ranks in Disable device all you need is one level as a Rogue or Artificer and enough skill points. Also, the 1d6 Sneak Attack Bonus comes in handy for a damage dealer as-well-as evasion if you take a second level of rogue. If you chose to take a level of Artificer for you DD, the ability to use rune-arms to increase your damage is also fair. Useful builds are for example:
- Rogue/Ranger or Bard - has enough skill points even with low intelligence
- Rogue/Wizard - enough skill points due to intelligence being main stat for the Wizard
- Rogue/Fighter - needs some intelligence (less if human) but benefits from Sneak Attacks; can be a very strong build for soloing; optional, you can cut down intelligence too and compensate with continuous levels as Rogue (every fourth/fifth)
One point of view may be, that the level of Rogue reduces the characters efficiency in his main class, but actually those all are improved Rogues who can disable traps without (bigger) cuts AND fight/cast.