This achievement is for collecting 200,000 Tale Coins. This is a bit of a grind but should be too much of a hassle. I would not focus on it too much until the end.
I do recommend completing Chamballoon 2 on each play through as it will net you MAD Tales Coins. There are 5 Levels and they are easily completed. Use Velvet to complete Level 1 and then Laphicet to complete levels 2-5. Laphicet just destroys it using Insubstantiality. It will net you 1,000-2,000 coins per level and a whopping 20,000 for Level 5 and you also get a bonus 400 from the Katz for each level(1-4) and 800 for Level 5.
The rest is best grinding Slash Beat 2. There are ways to use most characters 3rd Mystic Art and get S++ ranks which net a lot of coins as well. Eizen was my favourite for this. Upgrade his equipment so you have 7 Souls. Start off using Coercion, Last Throes and Eleventh Hour, this will stun the Dummy Twice, use the first 2 Break Souls and once the attack is over if you time Deceiving Pummel correctly you will stun it again(Try to use it once the flames in Eizen's shoulder start to lower). Then use all 3 break souls and activate Eizen's 3rd Mystic Art at the end for Mad Damage. If you nail this properly you will just get the Mystic art before the time runs out. It will take some practice.
If you are good at sliding puzzles and can complete those fast you can get a decent amount of coins from that but its not very efficient since an advanced puzzle will net you about 1,000 coins if you finish under 5 minutes. Standard takes about 2-3 minutes but nets lower coin amounts.
Stay away from the Card game. I found those to be too frustrating as it is very luck based as you need to get a lot of points to get a lot of Coins. You will likely only get 500-800 per game.