On that matter, it would be really nice if the boss in the horse-chapter would get some additional drawings when they are riding one of the characters but I would also understand if that is too much work.
Would make sense, I'll make some alt drawings like the weight gain boss.
On the topics of bugs etc: The horse boss seems to sometimes get caught in a loop where they will only use the "Good horse"/"Bad horse" attack which does no damage so they will eventually go down without a problem.
There's actually a bug in version 0.7.0 where debuffs/buffs that are meant to last multiple turns only last one turn. The Bad Horse debuff is supposed to trigger strong attacks by the boss, but since it only lasts one turn (instead of 4), the boss will keep reapplying it. Needless to say, it will be fixed in the next version.
The mummy boss seems to be almost unbeatable when your party is fully mummified, even with one character wearing the gear that negates mummification and max level, he outdamages my team quite easily. I'm not sure but I think a fully mummified party is basically softlocked against that boss.
There's actually two items that negate mummification (even if the character is already mummified), so you'll never have to fight the boss fully mummified. A fully mummified party indeed doesn't stand a chance.