Playing them face-up activates them, while face-down 'sets' them
" " The Right Hero for the Job " " Wise Man Neos " Jaden & Syrus " Believe in Your Bro " Jesse " Crystal Transcendence " " Rainbow Crystal Collection " Jim " Dig Site Inspection " " Major in Paleontology " Kagemaru " Unlocking the Power " " Victory of the Shadow Riders " Nightshroud " Dragon Force " " Forged Steel " Sartorius " Destructive Fate " " Magician's Scales " Society " "Invitation" to the Society " Supreme King " Dark Unity " " Ruthless Means " Syrus " Power Bond " " Room for Growth " " Small Roid Big City " " The Roids are Alright " Tania " Order of the Queen " " Welcome to the Jungle " Titan " Archfiend's Conscription " " Archfiend's Promotion " Viper " Cold-Blooded Tactician " Yubel " Consumed By Darkness " " Dark Creation " Zane " Cyberdark Scheme " " Cyberdark Style " " Forbidden Cyber Style Technique " " Power Bond " Other Andrew " Low Blow " Christine " Fusion Party

So, birds give it its ATK from Graveyard, beasts its DEF the same way and if you have at least one of each on the field this card is immune to card effects
Lastly, at the end phase, when you have a Yubel monster on the field and this card is in the graveyard, you can bring it back to your hand or special summon it back to the field to have some defence for the opponent's turn
competitive (and to protect its place among the best trading card games), restrictions and bans are used to rein in cards that create too much advantage too easily or shut down interaction in ways that make matches feel unfair
Despite not being able to use that Monster as Synchro material and negating that Monster's effect, it is still a very useful card for searching the deck