Eiyuden Chronicle: Hundred Heroes

You need to recruit Stadler and unlock the Drill: Mock Battle node in the Drafting Studio in order to start these mock battles. While you could start these roughly half way through the game it's recommended to do it much later when you've unlocked most/all of the characters.

Once you've unlocked Stadler you'll find him in the north western courtyard of floor 1 in your HQ, here you'll be able to play various mock battles similar to the siege events in the main game. They are fairly short and the basically act as tutorials for some more "advanced tactics", It's worth doing these later in the game when you preferably have all the heroes unlocked though as they give extra buffs and unlock extra abilities/units to use. There are also two War Troop Boosts available in the Drafting Studio, which it would be worth getting both of these first too.

Stalling the Enemy
Nothing too hard here, I ignored my troops on the sides and just moved Stadler up 1 space to join the army in the middle, just stay here and let the enemy come to you each turn for an easy win.

Mastering the Rear
The army at the top should be moving towards Stadler every turn, move Euma south away from the middle and your southern army up to the same spot, face your middle armies to the direction of the enemy armies as this will block them off and allow Euma to escape, just keep moving Euma away and blocking the enemy from reaching him until your northern army reaches Stadler.

Mastering Cavalry Legions
Armies consisting of only Cavalry can move 2 spaces at once, so use your army on the right to engage the enemy in combat while you move Kassius and Stadler within range for the next turn, from here you can just use Kassius's Provoke ability to keep them from running away, it's better to provoke than chase as if you're chasing them north they might still reach the escape point. Chase them if needed when you run out of Provoke uses.

Practical Training
I made no changes to my armies/units for this one, before you start move Kassius to the right then Nowa and Seign to the middle and start the battle.
Turn 1 - Move all your armies up 1 space
Turn 2 - Just wait here, let the enemy come to you as they will block off a third of their force at the back.
Turn 3 - Activate any buffing/attacking abilities you want and just wait in place again, I advanced with Kassius, Elektra and Goldwyn to make use of Nowa's Cross Boost ability.
Turn 4 and 5 - Use Kassius's Provoke ability on the enemies above them, heal with Elektra if needed.
Turn 6+ - Should just be clean-up, advance into the remaining enemies and use any remaining abilities if needed.

The Unfavorable Battle
For this one I made quite a few changes to my starting armies, first replace Goldwyn with Reyna and replace Marisa/Wayve with Ymir/Sumire. For the units I replaced Nowa's mages with more infantry, Reyna I went full cavalry, Ymir I replaced mages with archers and Elektra I replaced infantry with better infantry. For placement I put Bernard, Nowa and Ymir in the middle, Elektra, Kassius and Reyna on the right and Seign on the left.
Turn 1 - Use Meldridge's Scheme ability to immobilise the enemies below them, use Nowa's Cross boost then advance Nowa/Ymir/Bernard north. Activate Reyna's Tenacity ability and face her east, face Kassius north, activate Elektra's cavalry boost then face her south.
Turn 2/3 - It's hard to give exact directions here as the outcome of turn 1 is a bit different each time, but basically you want to use Seign's Focus attacks on the biggest group of armies possible, use Reyna's Tenacity for defense, use Elektra's Emergency Aid to heal if needed and use Kassius's Provoke to keep any northern armies from flanking team Nowa. For team Nowa just leave them there and let the enemy come to you, use Sumire's Rescue ability to heal if necessary.
Turn 4/5 - Again mostly just stay stationary, face an army to any direction an enemy can come from and heal if needed, from this point it's mostly just clean-up as most of the enemy armies should be pretty low at this point while ideally you'll still have 2 groups of 3 armies with almost full health still.