This is a small light-duty mallet.

Print the head in TPU 95A (I used https://www.amazon.com/dp/B0BXNWK6NS?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_1&th=1). It is important to have the middle part that connects to the handle at a low infill (like 15%). Otherwise it is difficult to insert the handle. The head ends should have more infill, e.g. 75%. This makes the mallet heavier. You can make the head softer or harder by varying the infill percentage. I recommend the infill at the end to be more than in the center, but less than 100%. With the 100% it may still be OK, but it is more sensitive to the flow rate calibration. To me, chances to get nozzle clog are higher with the 100% infill. Also, I recommend 0.6 mm nozzle for any TPU prints. No supports are required for the head.

The handle is split into two identical parts for ease of printing. This way no supports are required for the handle either. I printed using Elegoo Rapid PLA+, but it is probably not the best choice of this specific item. I'd recommend PETG, ABS, or ASA. Although, for ABS and ASA you may need brims to avoid warping. Because the halves have to join, they need to be printed on a smooth bed (like smooth PEA sheet). Alternatively, the handle halves can be sanded to make them flat, but it is an extra step. In the slicer increase the number of walls to make the neck solid without infill. Use superglue to join the halves. The connector is inserted between the halves and aligns them.

Once you have the head and the handle printed, push the handle into the head. Do it with steady and straight force. Avoid tilting as the narrow part of the handle may snap.  Before joining, check the slot in the head and remove any stringing in there.

The inserted handle is cushioned by the low infill of the middle part of the head, which reduces stress on the handle. Also, when the mallet is used, it is expected that the force of the strike comes from the weight of the head and not from pressing the handle. The handle is mainly to provide acceleration to the head.