A strong acid has a stabilized conjugate base. Oxalic acid is stronger than malonic acid because its conjugate base has much more resonance structures than malonic acid's conjugate base.

A classic example of a carboxylic acid decarboxylation occurs in the malonic ester synthesis. The malonic ester synthesis is a chemical reaction where diethyl malonate or another ester of malonic acid is alkylated at the carbon alpha (directly adjacent) to both carbonyl groups, and then converted to a substituted acetic acid.

Malonic acid is another example of an acid that will decarboxylate when heated (not sure at what temperature this happens, though)The structure of malonic acid is HOOC-CH2-COOH.

Malonic acid is a competitive inhibitor of succinate dehydrogenase.

Yes, it is diprotic, HOOC-CH2-COOH

it is a competitive inhibitor