An Arrow Effecting Item, Called The Pew Gun! It Unlocks When You Get Video Game Stuff (Meat Cube, Little C.H.A.D, Steven, Little Steven) It Increases The Firing Speed Insanely, But It Decreases The Damage. Its Visual Effect Will Make Isaac's Face 8-bit (his eyes will be pixels, and so will his mouth) The Shots Will Be Green.
Another Idea Is A New Tarot Card. "The Angels". When You Use It, You Get Wings, And All Enemies Take Damage. Your Arrows Will Be Replaced With Holy Beams (Fully Charged Chocolate Milk + Technology Effect) If Used On Mom, Mom's Heart, Or It Lives, Then It Won't Have Any Effect. If You Use It On Satan, It Will Reduce You To A Half Heart. (Same Effect As Chocolate Milk, Technology, XIII Death, And Lord Of The Pit) (Lasts Till You Leave The Room)
Next Idea: ???'s Charm. A Spacebar Item. Charges After 6 Rooms. It Converts All But A Half Heart Of Yours To Soul Hearts. Your Health Is Not Lost Though, Its Just Empty. VERY Helpful When The Level Is Littered With Hearts Before A Big Boss. Unlocked By Defeating The Fallen 3 Times (Including The Satan Fight)
Another Idea: Mr Meme. A Spacebar Item, Random Recharge Depending On What It Does. Its Effect Is Random, But It Can Do: Nyan Cat (Shoots Rainbows In 4 Directions, Similar To The Fallen, This Ability Charges From 2 Rooms) Creepypasta (All Enemies Are Turned To Stone, Charges From 5 Rooms) Arrow To The Knee (All Enemies Take Low Damage And Move Slower, Recharges From 3 Rooms) Mr Meme Unlocks From Beating Many Bosses, Any Of Them Count. I Don't Know The Average Bosses Beaten, So I Can't Really Lay Out A Good Amount.