Well, i'll list from most efficient to lowest efficient bosses to farm
Silver Tokens
:
The Scourge of Oblivion: (Also know as last library boss) 0~25, average of 12 each boss.
Ghulosh: 0~12 silver tokens, average of 6 each boss.
Gorzindel: 0~12 silver tokens, average of 6 each boss.
Lokathmor: 0~12 silver tokens, average of 6 each boss.
Mazzinor: 0~12 silver tokens, average of 6 each boss.
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Ferumbras Mortal Shell: 1~6 silver tokens, average 3 each boss.
Dream Courts Bosses:
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1~4 silver tokens, average 2 each boss.
Grave Danger Bosses:
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1~3 silver tokens, average 2 each boss.
Zelos: 0~4 Silver Tokens, average 2 each boss.
The Source Of Corruption: 0~3 silver tokens, average 2 each boss.
The Last Lore Keeper: 0~4 silver tokens, average 2 each boss.
Ferumbras Ascendant Quest Bosses:
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Average 1 silver token each boss.
There is a lot more bosses that drops silver tokens, but most of them have lower than 1 silver drop average... I'll list them here just for knowledge:
Thais portals bosses, cults of tibia bosses, warzones 456, urmalulu, werebosses (edron/cormaya), drume, kroazur, scarlett, ancient spawn of morgathla.