This is valid, but its also valid to wait to pay for the spell until the final step of casting a spell: 605.3a A player may activate an activated mana ability whenever they have priority, whenever they are casting a spell or activating an ability that requires a mana payment, or whenever a rule or effect asks for a mana payment, even if its in the middle of casting or resolving a spell or activating or resolving an ability
Better to be lucky than good, after all
(6/13/2017) If two or more effects require a creature to attack different players or planeswalkers, such as that of this scheme and that of Gideon Jura's first ability, that creature's controller chooses one to fulfill
These two critters are looking formidable with their battle-ready poses and improvised weapons
Squirrel Wrangler Squirrel lovers will go nuts for this one
The stock is made by a small number of mills and printed by large card manufacturers like Cartamundi under contract with Wizards