You can use Warriors from the Deck as Material which benefit from being in the Graveyard or can be easier Special Summoned there like "Buster Blader, the Destruction Swordmaster". It is also helpful for getting equip cards on your creatures for this card to send to the graveyard.
You can destroy this card yourself through "Really Eternal Rest". This way, if your opponent controls a monster(s) with equip cards, you can clear the field and special summon the monsters that were equipped to "Red-Eyes Slash Dragon" to attack directly with them all.
A good Fusion Material to use is "Amazoness Swords Woman", since your opponent will take any Battle Damage inflicted when it battles.
If your opponent tries to destroy this card, it will only result in you swarming the field. When this card is destroyed, revive it using the effect of "Red-Eyes Retro Dragon", while using "Slash's" effect to summon the Monsters equipped to it earlier. This way, you can expect to control at least 3 Monsters.