User blog comment:Degritone/Tonan, the Essence Thief/@comment-3542156-20141117122544/@comment-7709681-20141117190741

@ DBInitiate: Mana Burn is not entirely bad, is just that I don't think is an effect that no longer makes sense inside the game. Beyond the points I'll mention, I must say that the concept is now far more balanced than what originally was.

And so, the reasons that, in those games, makes sense, is because:
 * In the MOBA enviroment, Mana Burn currently exists only in two games (DotA / DotA 2 and HoN), what had they in common? All concepts use mana, whether or not abilities inside kits may cost something else (Much like, to us in LoL, Olaf and the old Sion did).
 * It was a really rare effect, barely represents the 10% of the total character pool in those games and, on each case, the effects were single targeted unless it was a damaging ult or a non-damaging basic ability (Or could have damage, but was minuscule).

Well, this is all that I could think off to help, at least I hope it helps.
 * It has guaranteed (100%) effectiveness, despite there are equally obnoxious effects such as Silence and Disarm (Which also exist in LoL), the thing at the effect's favor is that there wasn't a single character that wouldn't have mana. In contrast to the 83.5% affected targets (101) and the other 16.5% that counters him (20) that, in LoL, would have.
 * Isn't as effective as you may though, you see, in almost all the cases within those MOBAs Mana Burn is for a flat value and doesn't have a scale, with the exception of three that scale with the target's current or maximum; however, among all the cases some concepts repeat:
 * Doesn't affect that hard all characters, you see, characters that are mostly (if not entirely) autoattack dependants, have secondary resources (Only health in those games, beside mana that is) or have a plentiful amount of entirely passive abilities with few active abilities can match against the effects. Now imagine how horribly hard counter would be each champion that doesn't use mana against him.
 * High mana pools / mana regen. counter it, in those games such thing as itemizate mana or, even better, mana regen. (Which I argue is far more effective to counter it) isn't cheap, and commonly comes with defensive stats that don't synergyze with it, but doesn't stop to further help the player against the damage type, but what  I meant to counter the degradation of mana, also, making it somehow expensive allows Mana Burn to be a viable effect inside those games. On the contrary, not only mana regen. is cheap to itemizate on LoL, but also with the likes of Athene's or, specially, Tear of the Goddess and any of its upgrates would counter the effects really easy.
 * Single intances are weak and healthy, you see, rather than the effect per se being toxic it's the application that make it such, despite what I said --most of the cases are flat values with no scale-- commonly single instances of flat mana burn are sightly healthy (With the exception of percentual mana burn), and the reason is that this offer counter-play, as these are assured that the entire mana pool won't perish.
 * Persistent effect applications (DoTs or High DPS) are toxic, and the reason is that they don't offer no counter-play other than retreat, a form of harrass that can't be oppossed unless you don't depend of abilities, but if you do, then applies the general concept of toxicity of Mana Burn: Acts as a long term silence. Here you have four prospects for such argument.
 * An ability with persistent DoT Mana Burn.
 * An entire kit, in which each ability has or applies Mana Burn.
 * Mana Burn on-hit on a potentially high DPS character.
 * Spammable ability with Mana Burn.