You would need to pay 2R and discard two lands. The discard X lands is an additional cost to playing the card, the x in the casting cost is still how much mana you would need to pay.
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Commander: UBG Tasigur, the lab enabler UR Planeswalker Control UBRW Breya's personal box of combos BRW Vampire beats, by Dre 1 Karn, where all lands are command towers UBR Inalla's Venser lock UBRGW Atog Atog contraption tribal WUB Xur's second chance UGW Derivi, bird tribal R Brother's Yamazaki BRG Prosh, the scourge of multiplayer GW Capt. Sisay's Deck Dumping Service UB All Your Spells do Belong to Me UG Tapioca Pearl BG Meren's grinder
All Xs have the same value, whereever they appear on the card. So with X=2 chosen, you have to discard 2 lands cards and pay 2R.
107.3a If a spell or activated ability has a mana cost, alternative cost, additional cost, and/or activation cost with an {X}, [-X], or X in it, and the value of X isn’t defined by the text of that spell or ability, the controller of that spell or ability chooses and announces the value of X as part of casting the spell or activating the ability. (See rule 601, “Casting Spells.”) While a spell is on the stack, any X in its mana cost or in any alternative cost or additional cost it has equals the announced value. While an activated ability is on the stack, any X in its activation cost equals the announced value.
UBG Tasigur, the lab enabler UR Planeswalker Control
UBRW Breya's personal box of combos BRW Vampire beats, by Dre
1 Karn, where all lands are command towers UBR Inalla's Venser lock
UBRGW Atog Atog contraption tribal WUB Xur's second chance
UGW Derivi, bird tribal R Brother's Yamazaki
BRG Prosh, the scourge of multiplayer GW Capt. Sisay's Deck Dumping Service
UB All Your Spells do Belong to Me UG Tapioca Pearl
BG Meren's grinder
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