Rank 4 Xyz monster are very cool one of them is the one seen in zexal series Number39 Utopia a warrior monster with 2500 attack power and the effect of negating the attack by detaching 1 Xyz material so no worries if your opponent get to summon high level monster it still buy some time until you get the right card like ''Fusion Sword Murasame Blade'' which increase a warrior type monster by 800 Utopia become 3300 attack power over coming many of monster, now we come how to summon Utopia in your first turn by the effect of ''Kagetokage''and any level 4 monster  which summoned by it effect after that it changed to defense position 

If you are lucky you could have these three monster Goblindbergh,Kagetokage and Rescue Rabbit first summon Goblindbergh then it summon Rescue Rabbit and Kagetokage summon itself when you summon level 4 monster and in second your filed filled by 3 level 4 monster and you are ready to summon ''Number 10: Illumiknight'' rank 4 Xyz monster with the effect of sending 1 card to grave and draw 1 instead that come in help if you need new card and want send your card to graveyard to preform it effect from grave also it attack is 2400 which is good  incase you have warrior supporting card t o make it higher like  ''Fusion Sword Murasame Blade'' to become 3200 attack to take any monster out there.