Activate quick spells during the battle phase (i.e. Mystical Space Typhoon) to increase the ATK of this monster and win the battle (the quick spell itself does not need to have an ATK increasing effect). During your own battle step you can also reveal a "Pitch-Black Power Stone" and shift one of its counters to this monster to increase its ATK. This strategy can be used as well after summoning this card during battle phase with "Magician's Circle".
Summon this card, then use 4 permanent/equip/field spells then use "Giant Trunade" to give the spells back to your hand and activate them again. This way Cerberus gains 9 Spellcounters (1400 + 9x500 = 5900 ATK). If you additionally used "Terraforming" to search for a field spell you gain a 10 counter. And if one of your spells is "Mage Power" you gain additional 2000 ATK for the 4 permanent/equip/field spells. This way the ATK of "Cerberus" allready raises to 8400 points. Of course It would be increased further if the other spells would be ATK-increasing spells as well.