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The pre-recorded commentary clashes with the idea of the tournament. In the game, you don't get pre-recorded commentary about what guards you'll face. We're simulating in-game battles.
The biggest challenge with the timing is not knowing who will participate. If we had a definite roster, we could coordinate schedules, have some players play in advance, etc. But as it is, I don't know who will show up or how many people there will be until the last minute. And even if someone says they'll come, it's only a 50/50 chance. This has been repeatedly proven in many Heroes communities; everyone is a man of their word... in theory.
Added 4 hours 51 minutes ago
I've taken a break from these tasks.
1) Rampart. Here, you can get away with losing 4 peasants (99.35%). Arrangement: Grand Griffon - Pegasus - Knight - 1 peasant - 1 peasant - 1 peasant - 1 peasant.
The Grand Griffon, under the effect of Bless, and the Knights take out the upper-left stack. One peasant runs to hold the lower-left stack; the rest stand in the center, at the edge of the Naga's attack zone.
In the 2nd round, the Grand Griffon runs to the corner, the peasants run behind the Nagas, trying to lure them and the lower-right corner. In the 3rd round, the Grand Griffon and Knights take out the lower-left stack, the Pegasus flies to the lower horizontal, drawing the Naga's attention. In the 4th round and beyond, the Pegasus flies up and down, the Grand Griffon shoots, and the Knights finish off the enemy as needed.
Perhaps there's a way to get by with 3 peasants (99.51%), but I haven't tested it.
2) Inferno. Ideally, you can get away with 3 Imps (99.78%), but in practice, I managed with 3 Imps + 1 Demon (99.13%). Much depends on how the damage falls in the 1st and 2nd rounds.
Arrangement: Goblin - 1 Imp - Demons - Dogs - 1 Imp - Ifrit - 1 Imp.
In the 1st round, the Dogs and the entire group attack the upper-left stack, and the Goblins attack in melee (!). You need to take it down. This works about 2 out of 3 times. The single Imps run as low as possible, but so that the Nagas can't reach them.
The Nagas move, and the lower-left stack is positioned so that the entire army can attack it without being hit by the middle stack.
In the 2nd round, the army attacks the lower-left stack, the Goblins are already shooting. The only danger here is killing the Ifrit. After the Dogs and Ifrits attack in both rounds, there should be 2 Nagas left in the stack. The Imps run to the right and down, luring a Naga.
In the 3rd round, the Ifrits fly to the lower horizontal, luring a Naga. The Nagas are positioned nicely; you can hit 2 of them with the Dogs. But it's not recommended to use Bless on them; you need 2 Haste spells on the Ifrits; otherwise, they won't have enough movement points to control 3 stacks. You need to pull them up and to the right, not just up.
In the 4th round and beyond, the Ifrits control the Naga, and the Dogs and Goblins take them down. Sometimes, one Naga unit might rush to the left; you need to kill it. This is where I lost the Demon; the un-Blessed Dogs didn't have enough damage.
3) Barbarian. Losses achieved: 11 Ogres, 2 Wolves, 1 Goblin (90.98%). Arrangement: Bears - Rukh - 1 Wolf - 1 Wolf - 1 Goblin - Wolf - 11 Ogres (leave one in the garrison).
In the 1st round, 2 single Wolves remove retaliation from the left stacks, the Wolves with Bless take down the lower-left stack, the Bears and Rukh attack the upper-left. After the Nagas on the right attack, the Ogres run to the lower-right.
There, they successfully withstand 3 attacks. When their turn comes, the last Ogre removes retaliation and dies. The Nagas run forward, and the Wolves finish off the stack from which the retaliation came. The Rukh finishes off the upper-left.
Next, a slight problem arises: 2 retaliation attacks remain - Goblin and Bears, just on 2 stacks of Nagas, but the Nagas constantly run after the Wolves. Here, you need to find the moment when, with Haste or by chance, you can get the Wolves out of the 10-cell zone of the Nagas. This is quite feasible, although you might have to run around a bit. Especially, the Nagas get confused if you chase them up and down the right flank; they stick to the edge of the field, and Haste allows you to get out of their line of sight.
The achieved 90.98% is not too great; perhaps there are ways to get through without losing Ogres. But I haven't thought about that yet.
I welcome suggestions regarding the other castles.