Im slightly confused based on the wording of Urza's filter, which says multi-color spells cost UP TO 2 mana less to cast.
My question is does this mean that Urza's filter "see" other casting cost discounts and is limited by them?
Ie lets say I have both Urza's filter and Rhonas's Monument in play and I go to caste something like an Abzan Guide how much mana does it take to cast in total 1WBG or WBG
Like does it get discounted by one from Rhonas's Monument and then an additional two from Urza's filter or does the UP TO part of the filter mean that it "sees" the monument and only discounts it by 1 because that makes it's total discount cost 2.
Where Urza's Filter says "up to 2 less", it means the player casting a multicolored spell chooses how much Urza's Filter reduces the cost to cast that spell. It doesn't change how other cost reduction effects work. In this case, read "up to 2 less", as "0, 1, or 2 less" (C.R. 107.1b; see also C.R. 107.1c). (See also Training Grounds, which has a sentence that changes how its own effect works, not how other cost reduction effects work.)
For example, in the scenario given, if you cast Abzan Guide normally, it would normally cost 3WBG, but—
Rhonas's Monument reduces that cost by 1 to 2WBG because Abzan Guide is a green creature spell, and
Urza's Filter lets you reduce that cost further by 0, 1, or 2, your choice, resulting in a total cost of 2WBG, 1WBG, or WBG, respectively, because Abzan Guide is multicolored
(C.R. 601.2f). (However, if you cast Abzan Guide face down via morph, it will cost 3 and this cost can't be reduced by Urza's Filter or Rhonas's Monument, since the resulting spell would have no colors [C.R. 702.36a, 202.3, 601.2f]. Neither do Urza's Filter and Rhonas's Monument change how much you pay to turn a face-down permanent face up due to morph, since doing so is not the same as casting a spell [review C.R. 701.4].)
My question is does this mean that Urza's filter "see" other casting cost discounts and is limited by them?
Ie lets say I have both Urza's filter and Rhonas's Monument in play and I go to caste something like an Abzan Guide how much mana does it take to cast in total 1WBG or WBG
Like does it get discounted by one from Rhonas's Monument and then an additional two from Urza's filter or does the UP TO part of the filter mean that it "sees" the monument and only discounts it by 1 because that makes it's total discount cost 2.
For example, in the scenario given, if you cast Abzan Guide normally, it would normally cost 3WBG, but—