You stretch your hand and place all 5 fingers on any object you wish. Then the tips of your fingers glow, and your entire body begins to transform into the same material as the object.
As this happens, you gain abilities from certain objects: Metal(any): +5 armor class, +5 on your attack roll, -5 speed, you can't be pushed back (you must roll a D20 for strength and get a higher number than 15 to push back), and you get advantage on a saving throw against fire damage. These abilities are the same for stone and any hard material. For gold, you get disadvantage on fire damage saving throws.
Glass: +10 stealth, -6 armor class, -5 HP, and you get advantage to hit targets who don't see you.
Cloth(or any furry, soft surfaces): You don't suffer from the cold, you absorb water, you have a powerful grip (which can be used to climb) and you float easily.
Wood: You produce sap unlimitedly (which you can eat), you have disadvantage on any type of fire damage saving throws (and fire does more damage to you by 1D4), you start to grow leaves on yourself, and if you stay in water for 30 minutes, you begin to heal hit points. (If you are at max health, then you gain extra hit points that go away when taking damage). You gain hit points by rolling 1D8 for every ten minutes that goes by.
Magical gems (or gems): If you are hit by any type of magic, you can absorb the energy and throw it back at the enemy. The enemy takes 1D12 damage.