The transformation drains Mana Charge, leaving the remaining Manamune on 0 bonus mana. This can be recharged, and will transform into Muramana upon completion.
It is possible to charge a third Tear of the Goddess for a further 750 bonus mana. Note that the Awe and Insight passives of Archangel's and Manamune, and the transformation passives are unique and so further purchases won't provide anything beyond the base stats.
Muramana toggle ability is treated similar to on-hit effects.
This item, by itself, grants a total of 40 attack damage with its passive.
Also, by itself, the first hit of its active will consume 30 mana to grant 60 bonus physical damage on attacks and single-target spells.
There is sometimes a tooltip bug where the bonus AD from mana will "cap" at 80, however, the actual bonus AD from mana not capped and will still be granted.
While unstated in the in-game description, the item does not trigger on single target damage over time abilities, such as Torment, or non-damaging abilities such as Cocoon.
In-game description: "Single target abilities or attacks will consume 3% of your current mana to deal twice that as physical damage."
Multiple component spells which are calculated as single-target spells, such as Unleashed PowerSyndra, will proc Muramana's passive multiple times, in this instance this will result in additional physical damage up to roughly 38.4% of the champion's current mana.
There are a selection of on-hit effects that are classified as abilities, and will trigger Muramana's damage twice. The reason for this is Muramana is triggered once as an on-hit effect, and once as an on-ability effect. Typically, an ability will apply either on-hit effects or on-ability effects, but the following abilities apply both:
Devastating BlowPoppy and Pick A CardPick A CardTwisted Fate apply both on-hit effects and on-ability effects, like the above. However, the basic-attack component deals 0 damage. Unlike how Muramana will not trigger if an ability deals no damage (such as Cocoon), it will trigger if an attack deals no damage.
SunlightLeona and IlluminationLux will also trigger Muramana when the marks are consumed, potentially allowing for double-damage if they are triggered by a basic attack or single target, non-periodic spell.
With the exception of Urchin StrikeFizz, abilities that apply on-hit effects will only trigger Muramana once. Urchin Strike is an exception because it applies both on-hit effect and on-abilities effects, while all other examples only apply on-hit effects.
Muramana's on-hit passive does not proc life steal or spell vamp.