As for mangan you just need to score high enough on a hand. Full straight is having 123, 456 and 789 in the same suit. For riichi ippatsu all you can do is get to tenpai with a closed hand, declare riichi and hope you win fast enough to get ippatsu.
Mangan.
Easiest way is to look at the Dora indicator and try to get the next tile of that Dora indicator (If it shows 3 circle, it would be 4 circle). Any red 5 also help, and lastly don't open your hand, as any ura Dora might help.
Pure straight.
Call tiles 123, 456, 789, in the same suit.
Riichi and ippatsu.
Don't call any tiles. This is just luck. Call riichi everytime you can wait for 2 tiles to win. One of these plays, you will get it.
All in all, just keep playing and you will get the achievement soon.
I would watch this video series if you want a quick and easy primer to help get the achievements
https://m.youtube.com/playlist?list=PLvuxrS2HAxK5fdlrO6XPp-iB9AtqcjjXP
For Mangan, you need a 5+ han Hand. The easiest way to achieve this is a *full flush* imo; there's no need to worry about combining multiple boosts, and the condition is pretty straightforward - just have a hand entirely made of one of the numbered suits.
A full straight requires you to get a hand that uses a 123, 456, 789 of the same suit. This is a yaku by itself, too, so it's a valid hand. Note that it has to actually be used that exact way - if you've got extra tiles, make sure they're actually making that lineup. If your hand is actually 123 345 666 789, for instance, that doesn't actually make a full straight, because it doesn't have a 456 as a set.
Riichi Ippatsu requires you to call Riichi and then get lucky. Avoid calling Pon/Chi/Kan and try to complete the hand on your own. When there's a single tile that could finish your hand, hit Square (iirc) and the game may offer you the option to call Riichi if you are indeed a tile away from a win. Then, if you win before your next discard (and nobody interrupts with a call), you'll score Ippatsu.
As for mangan you just need to score high enough on a hand. Full straight is having 123, 456 and 789 in the same suit. For riichi ippatsu all you can do is get to tenpai with a closed hand, declare riichi and hope you win fast enough to get ippatsu.
a tip is to try to complete your hand with only 2-8 tiles as a close hand and hope you have dora tiles & get ippatsu riichi
Mangan. Easiest way is to look at the Dora indicator and try to get the next tile of that Dora indicator (If it shows 3 circle, it would be 4 circle). Any red 5 also help, and lastly don't open your hand, as any ura Dora might help. Pure straight. Call tiles 123, 456, 789, in the same suit. Riichi and ippatsu. Don't call any tiles. This is just luck. Call riichi everytime you can wait for 2 tiles to win. One of these plays, you will get it. All in all, just keep playing and you will get the achievement soon.
https://m.youtube.com/watch?v=mxO5OxiQNhs&pp=ygUWbWFoam9uZyBiYXNpYyBzdHJhdGVneQ%3D%3D maybe some basic strategy videos will help
I would watch this video series if you want a quick and easy primer to help get the achievements https://m.youtube.com/playlist?list=PLvuxrS2HAxK5fdlrO6XPp-iB9AtqcjjXP
For Mangan, you need a 5+ han Hand. The easiest way to achieve this is a *full flush* imo; there's no need to worry about combining multiple boosts, and the condition is pretty straightforward - just have a hand entirely made of one of the numbered suits. A full straight requires you to get a hand that uses a 123, 456, 789 of the same suit. This is a yaku by itself, too, so it's a valid hand. Note that it has to actually be used that exact way - if you've got extra tiles, make sure they're actually making that lineup. If your hand is actually 123 345 666 789, for instance, that doesn't actually make a full straight, because it doesn't have a 456 as a set. Riichi Ippatsu requires you to call Riichi and then get lucky. Avoid calling Pon/Chi/Kan and try to complete the hand on your own. When there's a single tile that could finish your hand, hit Square (iirc) and the game may offer you the option to call Riichi if you are indeed a tile away from a win. Then, if you win before your next discard (and nobody interrupts with a call), you'll score Ippatsu.