I would suggest this:
- Marius goes back to the secret doors and opens them
- Marius runs as fast as he can (he's a monk after all) back to you and climbs up to his ambush location
- Reynard waits with the dagger, I assume the beast will notice it as it comes closer - this should set it up for predetermined location
- I think most damage would (logically) be done if the beast takes the bomb in its maw where it is detonated - since we're not making powder keg worth of explosives, it should be targeted - but this could be hard to pull off (but think of the scene - Matrix - Trinity: Dodge THIS! Blam!) - this could maybe be something like:
ready action: throw the bomb, standard action: shoot the bomb
(maybe the bomb could be self-igniting by using one or more flares as part of the package?)
- Marius would like to jump from above and hit the beast from behind, possibly landing on its back (if it is quadruped) maybe pushing it prone
- any fire we can scrounge up (sap, lamp oil etc) can be ignited by his shuriken, various spells flares or Marius' elemental fist - but somehow we need to douse the beast in the flammables
(I suggest Gardener forms tight fitting passage throught the plants with oil sacks and fermented fruits set up along the path - smaller creature (Marius) could run without bursting them while larger/wider one would get dosed)
Don't you think it would be terrible if we prepared everything to fire the thing and it turns out to be resistant/immune to fire
EDIT: one more thing: hit it with everything you have, grit for damage, empowered spells, whatever. We may finish it before it begins if we're lucky
