Note that Tumblebuff does NOT work in current patch. There is no different method as of right now. Refer to Downpatching for further information.
The Tumblebuff is a glitch in Dark Souls III which enables the player to buff a normally non-buffable weapon with a resin, applying the full resin effect and additional damage on to the weapon
The glitch is achieved by using a Resin on a weapon that cannot be used, which stores the animation in the game memory proceeding by using a spell and a consumable afterwards to apply the resin to the non-buffable weapon.
Patch 1.08 and got patched in the pre-DLC2 patch but made its return on a later DLC2 patch: Patch 1.12Tumblebuff made its return on Patch 1.12, though only working with consumables with a fast animation such as Throwing Knives
Furthermore, Tumblebuff works with every Spell / Miracle now and is not restricted to Heal Aid.
Tumblebuff and Duping tutorial for Patch 1.12 by Nemz38
Tumblebuff and Duping tutorial for Patch 1.08 by PeachyMike