You activate Inferno Reckless Summon AFTER the monster has been Special Summoned. When Enraged Muka Muka is on the field, its effect gives it a power boost. This power boost is a Continuous effect, and becomes active after its Summon, and way before a player can choose to activate any cards (including Inferno Reckless Summon).
Because of this, before you activate Inferno Reckless Summon, Enraged Muka Muka's ATK is however much it is (3200, apparently). By observation, this is over 1500, and so you cannot activate Inferno Reckless Summon, because it needs a weak monster and Enraged Muka Muka isn't it.
Infernal Reckless Summon bases itself on the monster's current ATK. ATK/DEF modifiers (usually monster effects, Field Spell Cards and some Continuous Spell/Trap Cards) will apply themselves BEFORE you get a chance to play Infernal Reckless Summon/Bottomless Trap Hole/etc. So if the ATK/DEF is now wrong for the card you want to play, you cannot play it.
Another example: Umi is active on the field (amongst other things, it lowers the ATK of Pyro and Machine-Type monsters by 200). You Normal Summon V-Tiger Jet (1600 ATK). Umi's effect applies immediately, making V-Tiger Jet a 1400 ATK monster. Your opponent CANNOT activate Bottomless Trap Hole, because the Normal Summoned monster does NOT have 1500 ATK or more. It doesn't matter what the original ATK is; all that matters is the current ATK when you try to activate your card of choice.
Short answer - You can't activate Inferno Reckless Summon in this instance. See above for why.
Can anyone confirm?