Hello everyone and welcome to my 273rd analysis, this time featuring O'Reilly.
Overview: Great Base Speed and an awesome supportive movepool are huge pluses for O'Reilly, but what really puts him among the top dogs is Dodge Area. This is huge for a support, because not getting hit by a deluge of AOE debuffs really comes in handy when you're the one responsible for keeping buffs/debuffs in check. An AOE Stun is the cherry on top for O'Reilly to switch to denying should the need arise, making him one of the best Nature monsters in the game, as well as a fantastic team member for any team.

-Fun Dungeons
-He's Here To Help
-One Night Of Fun
Runes: 3 Speed/3 Team Speed
Mutant Rune options: Speed&Life, Team Speed&Team Life
Relics: Staves and Masks

Build Explanation:
Aye is an AOE Stun, which puts O'Reilly's great Speed to good use. Fun Dungeons is you ever useful AOE buff removal, and it applies a random debuff to all enemies too - so at the very least it's a buff removal, and at the most it's one of the most devastating AOEs ever. He's Here To Help is crucial to truly make O'Reilly an extremely flexible support. It costs 5 Stamina, has 1 CD, and it removes all debuffs from its target and gives them a random buff - remember that there are 3 different damage boost buffs in the game, so you're likely to get one of them fairly often. Lastly, One Night Of Fun gives O'Reilly just the offensive presence he needs by applying both Bleeding and Poison to all enemies, which not only makes them hit much less hard, but also damages them considerably over time.
3 Speed allows O'Reilly to move as often as possible and use Aye more effectively. Life Mutations are the standard on most monsters. However, 3 Team Speed with Team Life Mutations is perfectly acceptable.

Teammate Options: As with any Dodge Area monster, a Taunt monster is your best friend. O'Reilly's ability to do so much in terms of supporting makes him a desirable member for such a team, and in fact any team. For more Teammate Options , check out this article.

Countering O'Reilly: If you want to completely ignore O'Reilly, just pick an Artifact monster and you should be fine - Nitroblaster can ignore O'Reilly's attacks, then hit him with a Pierce assisted CD Activation when his turn comes. Otherwise, if O'Reilly's paired with a Taunt monster, having a Pierce monster or Trait Disable is absolutely crucial, because if you try to kill the Taunter, he can and will stop you from doing that whilst causing you great annoyance. For more Counter Options , check out this article.