>Evolved lilligant too early >Can't learn giga drain

Move tutor

>>27351565
In black/white?

>>27351357
That depends on what game you're playing. If it's BW, you're out of luck.

Move relearners can't teach your Pokemon moves that they never met the requirements to learn, so since you evolved it too early to learn Giga Drain, it won't ever be able to learn it and no move relearner will change that.

B2W2/ORAS move tutors will let you teach it Giga Drain, but that's it.

Or you could use something like an NDS Adapter Plus to edit your save.