The Chromatic Lantern letter says that the Lands you control have "Tap: Add one mana of any color to your mana pool.", My question is about the land of Rakdos Carnarium, add 2 mana but for the effect of chromatic lantern add 2 mana of any color or only 1 of mana
Any effect that adds an activated ability with just T in its cost to a permanent that already has one (as in your scenario) doesn't add any effects to the existing ability or otherwise change that ability. For example, in this scenario, Rakdos Carnarium's last ability doesn't become "T: Add BR. Add one mana of any color." or "T: Add two mana in any combination of colors", but rather, Rakdos Carnarium now has two separate activated abilities whose costs are each T (see also C.R. 112.2c). And paying the cost of one activated ability doesn't pay the cost for any other, even if it has the same text or the same cost (C.R. 117.10). See also this thread.
EDIT (May 10): Edited to conform to changes in Dominaria.
With a Chromatic Lantern in play, Rakdos Carnarium gains the ability to tap for 1 of any color, it doesn't change the exiting ability. You can add either RB or a single mana of any color. You can not tap it for 2 of any color/combination.
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Currently running in EDH: WUBRG: Karona - Chaos towards Divine Intervention ** WUBRG: Karona - God Tribal ** WB: Teysa - Angels, Wrath, and Return from GY ** UB: Szadek - Control and Mill ** RWU: Zedruu - Everyone Draws Cards ** BUG: Damia - Gorgon Voltron Ramp ** URG: Animar - ETB effects and Beatdown ** WUB: Sharuum - Lots of Artifacts UG: Edric - Tribal Rogues ** W: Odric - Tribal Soldiers ** B: Shirei - Shadowborn Apostle Deck ** RB: Tymaret - Kill all the things!
Any effect that adds an activated ability with just T in its cost to a permanent that already has one (as in your scenario) doesn't add any effects to the existing ability or otherwise change that ability. For example, in this scenario, Rakdos Carnarium's last ability doesn't become "T: Add BR to your mana pool. Add one mana of any color to your mana pool." or "T: Add two mana in any combination of colors to your mana pool", but rather, Rakdos Carnarium now has two separate activated abilities whose costs are each T (see also C.R. 112.2c). And paying the cost of one activated ability doesn't pay the cost for any other, even if it has the same text or the same cost (C.R. 117.10). See also this thread.
With a Chromatic Lantern in play, Rakdos Carnarium gains the ability to tap for 1 of any color, it doesn't change the exiting ability. You can add either RB or a single mana of any color. You can not tap it for 2 of any color/combination.
Thanks!
Notes: Two posts merged, quotes added to contextualize the replies.
EDIT (May 10): Edited to conform to changes in Dominaria.
WUBRG: Karona - Chaos towards Divine Intervention ** WUBRG: Karona - God Tribal ** WB: Teysa - Angels, Wrath, and Return from GY ** UB: Szadek - Control and Mill ** RWU: Zedruu - Everyone Draws Cards ** BUG: Damia - Gorgon Voltron Ramp ** URG: Animar - ETB effects and Beatdown ** WUB: Sharuum - Lots of Artifacts UG: Edric - Tribal Rogues ** W: Odric - Tribal Soldiers ** B: Shirei - Shadowborn Apostle Deck ** RB: Tymaret - Kill all the things!
Thanks!