TCG Rulings

• If you send a Level 5 or higher monster to the Graveyard to Special Summon Egotistical Ape, you cannot activate the effect that lowers its Level.^[1]

• You can still Special Summon Egotistical Ape while Zombie World is in play, however you will not be able to activate its effect to change its Level because the Beast-Type monster is being treated as a Zombie-Type monster.^[1]

• Even if the Beast-Type monster you sent to the Graveyard is no longer there when the effect of Egotistical Ape that changes its Level resolves, Egotistical Ape's Level will still change accordingly.^[1]

• If Skill Drain is activated while Egotistical Ape is on the field, it will become Level 5 again and remain Level 5 even if Skill Drain is later removed from the field.^[1]

OCG Rulings

• "Egotistical Ape" is a Special Summon monster.^[2]

References

1. ↑ ^{1.0 1.1 1.2 1.3} Konami Gameplay FAQ: Duelist Revolution Sneak Peek -- Card Rulings (Version 1.0)
2. ↑ Konami FAQ: Effect Monster > Egotistical Ape