This is a pretty rough overview of the routing I planned for THoT when I last ran it. I figured it would make sense to share for other people to use/build upon

Scenario 1 (At the East Gate)

Turn 1: Gryphon Rider -> village Recruit 2 Dwarvish Scouts Recruit 4 Dwarvish Fighters

Turn 2: Gryphon Rider -> hold Move 1 Dwarvish Fighter, repeat recuirt (Might not be needed on Easy/Normal?) Move full army east (slightly south, but not to far)

Fight around the village in the center of the map. Don't end turn next to forest unless an orc can't get onto that tile. Ignore villages unless you need to heal. Give kills to Leader and any other intelligent fighters you got. Try to keep gryphon alive.

Should have 1 Steelclad or 2 fighters <8XP from level up by the end of the scenario

Scenario 2 (Strange Allies)

Recall any fighters with <16XP to level up. Max 12 recruit/recall, 11 is fine in most cases, 10 can be risky on Challenging.

Move full army east taking the north route. Need to distract part of the army or the Orc leader will die. Rush base at first opportunity. Feed kills to Witness if possible. Should have multiple Steelclad an at least 1 with <24XP to level up.

Scenario 3 (Troll Bridge)

Max 6 recruit/recall. Recall fighter if <16XP to level up. If you recall Steelclad, only do 4 other recruits.

Stay on the Village/Hills in center of map, pick off Trolls at the edges or that take a lot of damage. Use Witness slow to keep units healthy while attacking. Witness should be level 2 by the end of the scenario.

Scenario 4 (Invaders)

Recruit/Recall 2 bases. Recall all Steelclads and any Fighters with <16XP to level up. Recruiting a few scouts is good for controlling damage taken during offense, too.

Send full army northeast. Fight to control the river and hills between Blue/Green base. Rush Blue/Green when you get the chance, then head south to Purple.

Bandits will appear in any unowned village, so leave some of the village near you base untouched so that Purple activates more bandits if he beats his first wave.

Should have at least 2 Lords by the end of this scenario, including Leader.

Scenario 5 (High Pass)

Turn 1: Scout with Witness. If you see a double Wolf spawn (on any turn, really), reload scenario. Recall 2 Steelclad Recruit 2 Dwarvish Fighter

Turn 2: Recruit 2 Dwarvish Fighter (or, situationally, Guardsman)

Try to get Leader around the opponents so he can run straight for end. South is better so he doesn't get ZoCed by gryphons. When you get to Perrin, keep him in the nearest village. Should end with Witness <16XP to level 3.

Scenario 6 (Mages and Drakes)

Recruit 2 Guardsman, 2-4 Thunderers. Rush (fight starts at night, so you don't take enough damage to be worried). Witness should be level 3 by the end of the scenario.

Scenario 7 (Fear)

Don't recall Lords, but do recall 3-4 Steelcalds. If you kept the gryphon alive recall it and use it to capture all the villages in the north (otherwise use a scout). Recruit 1 Mage. Maximum 2 bases of recruit/recall.

Send the mage south to capture villages until the berserkers are dead. Use Witness' "Inspire" to buff entire frontline during each turn (move him up and down as needed, don't attack until last). Feed the mages to get level 2 on both. Both advancements should be White Mages. Mages are best bet for taking out guardsman.

Once the gryphon is done taking villages in the north, distract units by moving him close to the enemy base (it's okay if he dies during this scenario).

The enemy has enough income to recruit 2 units per turn without villages, so you need to press forward despite resistance. The early finish bonus matters.

Scenario 8 (Forbidden Forest)

<110 starting gold: Good luck ~120 starting gold: Recall 2 Steelclad, recruit 2 fighters, recruit 2 guardsman (or recall level 2 if you have them) ~140 starting gold: add to that either a Mage or another fodder unit. Mage + Inspire melts Woses. Fodder unit can play riskier around blue. ~160 starting gold: add to that both Mage and fodder.

Use the forest edge along the path to bait Green onto flat terrain to take out units as quickly as possible. Then use east/southeast edge to do the same for Blue/Purple. Move Leader/WItness (and extra if Steelclad/Lord if possible) when you get an opening. Usually north will open up first.

Try to keep loyal mage alive. Scenario end when both Leader and Witness are within 1 tile of sign post at the same time. If Leader health is low, consider using Witness to slow dangerous units to keep them away from Leader.

Scenario 9 (The Siege of Kal Kartha)

Recall 2 Lords to send with Witness to attack North. Recruit/Recall 2 Mages (including loyal one, if it's alive) + 1 Lord + fodder on any extra base slots to rush Middle and then South leaders.

Only goblin scouts will bother moving west to attack you, everyone else moves east. Need to win fast before Kal Kartha falls.

Scenario 10 (The Court of Karrag)

Use Dulcatulos (the Steelclad) to take out the berserkers (free XP, he needs to stay alive so might as well make him a Lord). Use Witness to block if he takes too much damage. Should be over by turn 3.

Scenario 11 (The Underlevels)

I don't have a dedicated opening strat for this scenario (but I probably should). Break Green as fast as possible, otherwise you get bottlenecked and can't win in given turns.

The paths to Purple/Black are also pretty bottlenecked. Try to lure level 3 guardsman out so you can get more than 2 attacks on them per turn. There's no villages in either tunnel either, so use White Mages for healing if you have them. If you have only 1, send Witness down the other tunnel.

Last part of the scenario is pretty standard. Be careful that the teleports work both ways, so fast movement doesn't really work here.