Q: Dear Sage
Since the warlock's powers are innate, does he still have to train every level to gain his invocations (like a wizard learning new spells) or does he just get them automatically when he gains a level?
A: Dungeons & Dragons assumes that all characters are constantly training in their abilities, and that new class features, spells, feats, and so on are automatically gained upon reaching a new level without the need for special training costs.
The Dungeon Master’s Guide provides options for DMs who wish to require formalized training for characters to improve their abilities (DMG p197). It’s perfectly reasonable to require a warlock to train in order to master a newly gained spell-like ability just like any other arcane caster. Ultimately, however, it’s up to the DM to decide how to apply this optional rule to classes not found in the Player’s Handbook.
About the Author
The Sage is a mammal classified in the bear family, Ursidae, native to central and southern China. Debate continues as to whether he is truly a bear or more related to the raccoon rather than the bear, or perhaps in a family of his own. When not eating bamboo and answering rules questions, he works under the nom de plume of Andy Collins as an RPG developer in Wizards of the Coast R&D, where his development credits include Complete Mage, Dragon Magic, and the Player's Handbook v.3.5. He can be easily recognized by his large, distinctive black patches around the eyes, ears and on his rotund body.