I have a feeling this tactic will come up again. In RoT and down the road. Setting the rules straight for this will be a good for future campaigns and encounters with my group. I am most likely over thinking things...
What I plan on implementing is the following process that consists of two parts:
1.)
Getting to the creature to position oneself. That is first part. (Misty Step is fine, provided the PC can see where he is going.) This could be done by lowering a creature by rope, jumping, etc..
2.)
Then opposed ability checks in a Skill Contest to stay in that desired position or hold on, what have you. This means the PC and the creature now occupy the same space. Using the DMG rule from page 271 the Skill Contest would be between the Creature's STR vs PC's STR (Athletics) or DEX (Acrobatics). This would require use of the players ACTION for the round.
That part makes more sense now and is a minor change, but will eat up the PC's ACTION for that round. Thanks to those that referenced the DMG rule on climbing larger creatures.
QUESTIONS:
What to do with a failed Ability Contest roll here? The PC failed to occupy the same space as the dragon in the Contest. What about when the dragons turn comes around to move and the dragon is flying? Technically, the PC would not be occupying the same space therefore he would fall. This is the HIGH risk and HIGH reward part I guess and would make this tactic even more dangerous/heroic.
What about using one weapon or a two handed with shield for attacks while in position? The tough DM would say one handed weapon would
not require a DEX check while using a two handed or sword/shield
would require a DEX check. Fail would mean attacks at disadvantage for that round. I am thinking to keep the rolling down to a minimum of just skipping this part.
What happens from a Failed Save from Wing Attack? I really like the idea of Using the Wing Attack (Legendary Action) and if the PC fails his DEX Save of falling prone on the dragon. He has the condition of prone. At the beginning of the PC's turn he can chose to attack from prone with disadvantage or "stand" (positioning himself) and have to succeed at another Ability Contest of Creatures STR vs PC's STR (Athletics) or Dex (Acrobatics) to do so. With success he can attack as normal. This will eat up another action of the PC and draw out the combat. Additionally, I like the idea of if the PC is already Prone and suffers another effect of Prone, he would fall.
Dragon Shaking off PC The dragon could use its ACTION to attempt to shake off PC with contested Ability Rolls of STR vs PC's STR(athletics) or DEX (acrobatics). Failure would result in PC potentially falling. I would grant a DEX save to avoid falling, probably in the 16-19 range. If PC succeeded he would be PRONE for the beginning of his next round. My question here, is that dragons are really tough in 5e. Should that contested ability check replace his whole Multi Attack for that round or replace one of its three attacks from its Multiattack? (Bite and two Claw)
Everyone has been great and has given me a lot to think about. Look forward to your replies.