Sneak Attack [Double Masters] CRU084 the player can activate mana

the player can activate mana abilities only if they're from lands that player controls and only if mana they produce is spent to activate other mana abilities of lands the player controls and/or to play that card

Memnarch understands

Set: Double Masters Type: Artifact — Equipment Rarity: Mythic Cost: {3} Equipped creature gets +2/+2 and has protection from red and from blue

You gain 2 life

Sneak Attack [Double Masters] CRU084 the player can activate manaSet: Double Masters Type: Enchantment Rarity: Mythic Cost: {3}{R} {R}: You may put a creature card from your hand onto the battlefield. That creature gains haste. Sacrifice the creature at the beginning of the next end step.