
I won't pretend that there are any truly F2P-friendly gacha games out there, but some are easier to play than others without spending money. If you aren't a PvP diehard, then Umamusume: Pretty Derby is a good choice, with free shortcuts to obtaining your favorite horse girl and a focus on powering her up through training and support cards.
It's perfect for someone like me who gets their PvP fun elsewhere. I just want my gacha as a little second-screen, crunchy numbers treat. It's helpful that the auto-advance option works for most things in Pretty Derby, too, so I don't spend a lot of time babysitting my umas and grinding out F2P rewards.
I don't mind dropping a few bucks here and there whenever there's something I really want, but I've got a few tips as someone who's a (mostly) F2P Umamusume: Pretty Derby player.
Umamusume carats: How much does it cost to pity?
First tip: Let go of your PvP dreams. Even by modern gacha standards, Umamusume's running a pretty brutal pity system, so focus on enjoying your favorite uma and Career Mode. Since falling in line with a strict meta is only important for the top PvP players anyway, you're better off making peace with whatever support cards RNG delivers.
Umamusume's pity system lets you select a support card after accumulating 200 support exchange points. The real kicker is that those points don't carry over between banners—they're converted into yet another currency for use in the Pretty Derby shop.
Assuming RNG doesn't bless you with an SSR and that you have no discounted daily carat allowance, it's around $420 in carats to obtain your chosen support.

Start strong by rerolling accounts for better support cards

Gacha veterans are painfully accustomed to ritualistic rerolls—the practice of making a new account over and over until you get better (or at least mildly acceptable RNG) with free starter currency and resources. It's not good advice for anyone who's already sunk days or weeks into their account, but if you're starting fresh and have time to kill, it doesn't hurt to try.
You're given one free 3-star Voucher Ticket for an uma of your choice after completing the tutorial, and a handful of carats along the way. With the fresh supply of starter carats, don't roll on any more horses (that's what the voucher is for), and focus on pulling good support cards from the current Pretty Derby banner.
Every new banner won't be worth the account min-maxing hassle, but I cannot stress enough how wild Umamusume players are for the Kitasan Black card, so maybe time your strategic account rerolls for her beefy speed boost. This is my most take-it-or-leave-it piece of advice—I only made a few accounts before burning out on the process.
Prioritize limited-time stories and events for free carats

Umamusume Stories are individual events tailored to each uma and reward 20-50 carats per episode. They aren't time-gated if you own the character, but it's not like F2P players have a stable full of horse girls, so you'll have to make the most of Pretty Derby's limited banner freebies.
When new event banners kick off, the racing gacha lets you complete the featured uma's first four episodes while she's in the 10 to 14-day rotation. That's 80 free carats, and there are usually a few banners running at a time.
Event stories and special missions are the more time-intensive tasks with event-specific points, milestones, and rewards to grind out. You'll have to make serious progress in Career Mode to unlock everything, so make these a priority over other chores.
Spend your RP, but take Umamusume PvP losses on the chin

It's tempting to shoot your shot at climbing the Umamusume PvP ranks, but that's where Pretty Derby easily turns into a money sink. Team Trials are fine to horse around in, and even a bit of fun if you enjoy some of the stat crunching in the early ranks. I just have to remind myself that no amount of carefully planned freebie pulls and spreadsheeting can beat Umamusume's biggest whale.
Thankfully, Pretty Derby doesn't saddle you with a long list of PvP daily missions, so it's not a long grind. All you have to do for the regular allotment of monies and carats is participate—win or lose, you still receive freebies. Do enough to spend down free your RP (the Team Trial allowances that restore over time), but don't use any carats for more tries.
Do your chores and keep an eye on TP

'Do your dailies' is universal gacha wisdom, but I'll remind you again since Umamusume's daily missions only reward 30 carats. If you're saving for an upcoming 10-pull, you'll need 1,500 of the premium currency.
Daily missions also spend your allotment of TP. Just like RP, the Pretty Derby energy currency restores over time, so keeping it used up means you aren't overcapping and wasting hours of free resources. As a F2P player, I avoid wasting carats on more TP or extra Team Trial attempts. It's easy enough to bank a few restoration items from the shop and keep your carat stash saved for the next banner.