i use this combo, set one gandora when you got 1 card on top of your deck. Pro: you can destroy any thing that may break your combo, it annihilates traps, insta spells etc. your assestment will be more than 9000, because you may eternal activates gandora effect, cause Northwenko cant be destroyed if you targeted gandora when ritual summon her. Con: destroy 7 cards on the field.
It's quite easy to farm Mai. What you need is cerberus (2 copies), a lot of spell card (i use burn spell to decrease his LP & healing spell to increase my own LP) and as finishing blow either vassal with union attack (2 copies) or piranha with riryoku (1 copy) Both will get you 9999++ attack