Plat Farming

Source

Mobs known to drop coins:
LEVELS 0-19:
RHAATHUL THE CORRUPTER (3-dot, 8 mob in Ksaravi Hollow in Khal in Qalia)
SULUDYN (3-dot, 10 mob in Serpent of Sihari in Lomshir in Qalia
MASTER UIZA-DO KAHN (3-dot, 10 mob in Ra'Jin Stronghold in Kojan)
FOREMAN SNARLBACK (4-dot, 11 mob in Orcbane Mines in Vault of Heroes in Thestra)
XAOXIN (4-dot, 11 mob in Riftseeker's Torrent in Thestra)
XATHOK (4-dot, 12 mob in Riftseeker's Torrent in Thestra)
KAON BROODMOTHER (3-dot 11-13 mob in Arcanium in Leth Nurae in Thestra)
LALEN FRAE (2-dot, 15 mob in Veskal's Exchange. Pops after completion of "The Cure" quest series)
CLAN CHIEF BARGORG (2-dot, 19 mob in Stonecrushers Enclave in Three Rivers in Thestra)
KING JURDIN THUNDERAXE (5-dot, 19 mob in Khegors End in Thestra)

LEVELS 20-29:
ELBARION (5-dot, 21 mob in Fallen Lyceum sky part in Kaon's Rush in Thestra)
AMONIR (5-dot, 21 mob in Fallen Lyceum sky part in Kaon's Rush in Thestra)
MORWAEN (4-dot, 21 mob in Fallen Lyceum sky part in Kaon's Rush in Thestra)
Kalendra the Dark Witch (5-dot, 22 mob in Kalendra's Coven in Skrillien Point in Qalia)
OVERKING BARRAK (5-dot, 23 mob in Rekk hobgoblin valley in Renton Keep in Thestra)
GRAND TYRANT MILAS (5-dot, 24 mob in Ksaravi Gulch in Qalia)
RUL'ALOUK THE SOULSCORCHER (5-dot, 24 mob in Imanjal Sacellum in Skrillien Point in Qalia)
Mistress Anaya (4-dot, 24 mob in Hillsbury Manor in Misthaven Crossing in Thestra. Last part of questline there)
Mistress Bella (4-dot, 24 mob in Hillsbury Manor in Misthaven Crossing in Thestra. Last part of questline there)
Mistress Raylia (4-dot, 24 mob in Hillsbury Manor in Misthaven Crossing in Thestra. Last part of questline there)
Kill Kronus in CIS and 3 adds pop. Each one is 2-dot, 28-29 mob and can drop coins
Ageless One (x-dot, xx mob in CIS in Qalia) (need better information)
QUEEN AYXLXYX (5-dot, 26 mob in Ant Mound in Renton Keep)
VELETHEZOK (5-dot, 25/26 mob in Skrawlra Rock in Qalia. Needs to be summoned by collecting 3 different color masks)

LEVELS 30-39:
Nishek (6-dot(?), 31 or 32 mob in Trengal Keep in Thestra. Summoned, need whip from TK6)
THURRE (5-dot, 34 mob in Zossyr Hakrel in Qalia)
ZYFUUR (5-dot, 35 mob in Cragwind Ridge in Qalia)
GORLASH TOXIL (5-dot, 37 mob in Dargun's Tomb in Thestra)
BAHAR'NIHAB THE REAPER (6-dot, 37 mob in Fields of Despair in Thestra)
SOLATHUS (6-dot, 38 mob in Ruins of Vol Tuniel on Thestra)
YALSYL VONALYS (6-dot, 38 mob in Thelaseen in Thestra)
HIGHLORD SHO'DAR (5-dot, 38 mob in Thelaseen in Thestra)
MYRION THE PURE (5-dot, 38 mob in Spires Keep in Thestra)

LEVELS 40-49:
HIGH COMMANDER RAKH'YOR (6-dot, 40(?) in Greystone in Thestra) (exact level needed)
HRUK (6-dot, 40 mob in Karrus Hakrel in Qalia)
TAJIIHOSK (6-dot, 41 mob in Karrus Hakrel in Qalia)
OBSIDERRU (6-dot 40ish summoned mob in Karrus Hakrel in Qalia. Needs 30 aqual orbs for summon) (exact level needed)
DRILLLZARAX (6-dot, 41 mob in Islands of Madness in Qalia. Mob pops in tower)
HIGH TORMENTOR ZERAXEZ (6-dot, 42 mob in Vi'rak lair in Thestra(?))
XAALESEESH THE INFERNO (6-dot, 42 mob in Vi'rak lair in Thestra(?))
Overwarden Ehu Dal (6-dot, 44 mob in Sunset Pointe in Qalia)
Warlord Khurang (6-dot, 44 mob in Sunset Pointe in Qalia
Father Xennu (6-dot, 45 mob in Mind's Crown in Qalia)
Naxxillar (4-dot, 45 mob in Mind's Crown in Qalia)
Exxilar (4-dot, 45 mob in Mind's Crown in Qalia)
Araxxishar (4-dot, 45 mob in Mind's Crown in Qalia)

LEVELS 50+:
Majordomo in RI in Qalia (dot + other info needed)
Warlord in RI in Qalia (dot + other info needed)
ALUUL (6-dot, 53 mob in RI in Qalia)
DJUUL (6-dot, 53 mob in RI in Qalia)
SHALUU (6-dot, 53 mob in RI in Qalia)
KHORR (6-dot, 53 mob in RI in Qalia)
Hegnerian in swamps in Thestra (dot + other info needed)
King Mnalus (6-dot, 50 mob in swamps in Thestra)
LORD FALADRIEL (6-dot, 50 or 53 mob in Flordiel, Thestra)
Queen Vixxaeva in swamps in Thestra (dot + other info needed)
PHAROAH SHEKHAN NKOSA (5-dot, 51 mob in Nusibe Necropolis in Qalia)
Godking (x-dot, xx mob in Nusibe Necropolis in Qalia) (dot + other info needed)
Nepherit (6-dot, 50 mob in TOT temple before flip in Qalia)

50=6 dot last of the flipped names in TOT in Qalia (name needed)
RAFFEN (6-dot, 53 mob in Old Targonor in Thestra)
AKANDE (6-dot, 53 mob in Old Targonor in Thestra)
SHORUL (6-dot, 53 mob in Old Targonor in Thestra)
CENNFAR (6-dot, 53 mob in Old Targonor in Thestra)
NARANDA (6-dot, 53 mob in Old Targonor in Thestra)
TEKAR (6-dot, 53 mob in Old Targonor in Thestra)
CHATH + his pet (6-dot, 53 mob in Heroes Plain in Thestra)
SHADOW (6-dot, 53 mob in Isle of Shadows in Thestra)
SYD (6-dot, 53 mob in SOuthern Stonepie Ridge in Thestra)
STRIFE (6-dot, 53 mob in Ridge of Memories in Thestra)
TISHRA (6-dot, 53 mob in Gorgalok in Thestra)
Kronax (x-dot, xx mob in Umyebum Crypt in ToT in Qalia) (dot + info needed)

I have to share a little-known trick here... or at least not well-known!:

When you are fighting a mob that drops platinum coins hit ESC to de-target it just before it dies... I dunno why... but if you let the DoT's finish him it and de-target it, you can sometimes get 3-5 platinum coins per kill! I've never been one to get more than 2 per kill (and 2 only rarely!) until I tried this - now I'm regularly getting 3+ per kill!