Timely Reinforcements is more side-board than main, but that aside it's an excellent card that's very strong. It's kind of a meta choice. If you have a LOt of burn and Zoo decks in your area it'd be worth running, and there are a few easy things to cut for it:

Slaughter Games if you don't have to deal with combo.

Reat in Peace if there are no GY shenanigans.

Stony Silence if you don't really have to deal with artifacts.

Don't mean to bog you down with all my comments, just wanted to share my favorite "anti-burn" card. Vampiric Link. Throw that on an Eidolon of the Great Revel and laugh.

Have you tried any tinkering with Timely Reinforcements? Might help with all the self inflicted pain as well as the typically low creature count.

Saw your mardu list on reddit and had 90% of the list. I decided to pick up what I didn't have and throw it all together. I can say that this is one of my favorite decks to play so far. If I happen to find any additions or changes I truly like, I'll be sure to share with you.