By the request of a Tumblr user who wishes to remain anonymous, I bring to you a guide for Chase!
Have there ever been times where you were doing well on Item Hunt only to have that evil blue rabbit Chase ask you for some outlandishly expensive item? Do you still hate him for any of those moments? The good news is that you can get revenge on him in the Battle Coliseum. He is unlocked by failing or quitting Item Hunt on level 75 or higher (making him one of the most expensive challengers to unlock). Do note that this means that you can complete level 74 and then quit after he asks you for something on level 75 (though I'd still complete it if the item in question is under 300K or if you want the level 75 achievement).
As much as you want to beat up this douchebag, please note that he is one tough cookie. In fact, he is classified as "impossible" difficulty and is easily the hardest tier 11 challenger (I'd say his difficulty is about halfway between Malerias Familiar and Erupting Forj). Freezing is disabled against him, so don't think chaining Psycho Smashers and Shrieks of Despair will help you win. His stats are as follows:
Health: 13,750
Attack: 4,500
Defense: 3,000
Speed: 4,000 (formerly 2,500)
EXP: 3,777
His stats don't suggest too much difficulty compared to other tier 11 challengers, but they are kind of misleading. There can be a luck factor due to his ability to steal and a weapon set that has a weapon that can throw you off regardless of what main two weapons you use. His weapons are as follows:
Bored Silly: 10 or 15 fire, 10-40 light
Blocks 4 dark/water/fire/earth/wind/ice/magma
May activate Blue Bunny Shield Smash curse (25 icons; 1 round)
Boulderdash: 7-77 wind
Blocks 4 dark/water/fire/earth/wind/ice/magma
Gilded Swashbuckle: 10 physical, 12-25 light, 9-14 magma, 7-14 wind
Blocks all light/physical
Heals 350 HP
Generates one Gilded Item Hunters Bomb
Note: Damages you for 7% of your max health instead of healing you if you use this against him.
Gilded Item Hunters Bomb: 7 or 11 fire/light, 7 physical/earth/wind/water/ice/magma
Activates Golden Sear curse (7 icons; indeterminate duration)
Semi-breakable
Hopping Mad: 10-20 earth, 10-25 fire, 5 or 15 water
Blocks 5 earth/fire/magma
Boosts attack and defense by 50
Whip Smart Scroll: 5-11 fire, 6-7 light, 4-11 magma, 2-5 wind
May steal
Chase's icons are kind of all over the place. He has a potentially very large pure wind attack with his Boulderdash, he can do a lot of light icons with his Gilded Swashbuckle and/or Bored Silly, he can throw earth and water icons into the mix with Hopping Mad, or he can just do a little bit of almost everything with Gilded Item Hunters Bomb. Wind, light, and fire seem to be the best icon blocks. It is recommended that your weapons do not rely too much on light or physical icons since his Gilded Swashbuckles can completely block those two icon types (which the swashbuckle seems to be his most common weapon). The one factor about him that can be especially annoying is his Whip Smart Scroll since it is not uncommon for its stealing effect to activate at least once in a battle.
When making a set for him, I would recommend having three main infinite use weapons instead of two. This is so that you fare better against him if he steals one of them as well as to give you more ground for countering his weaponry. When you blast or steal his weapons, it may be a good idea to pay attention to which ones you take as to know which two weapons to use since he is now less likely to use whatever you just stole/blasted and there is now less emphasis on the weapon you would use to counter that particular weapon of his. Paintbrush Blades and Blessed Trident (or Swashbuckle) are ideal choices for two of the weapons you use against him. With the Paintbrush Blades + Trident example in the previous sentence, you will want to choose whichever weapon of yours is the overall best at countering his Bored Silly and Hopping Mad (Possessed Bow or Prodigy Staff are ideal options if you have one of those, and Natasha is an even better option than either of those two due to it generating stealing bait for him). Your weaponry setup doesn't have to exactly be that (I mostly listed that example because Possessed Bow + Trident + Paintbrush Blades is the most ideal combo my armory has to offer), but the general point is to choose three of your best weapons for countering various weapons in his set.
Like other high end challengers, it still helps to prepare for worst case scenarios by carefully choosing your scrolls and keeping a good supply of potions on you. Sancturia Exodin Scrolls are much more helpful than Cobalt Eternal Scrolls for Chase since he likes to deal a lot of light and even water is a bigger concern than ice icons. However, cobalts are still better than nothing. Typhoon of Valor or Perilous Whirlpool scrolls can help block a lot of wind or fire respectively if you desire lower budget options (neither scroll is very expensive to make). Morosbane or Lucky scrolls are not worth it since their pure light attacks can be completely eaten by his Gilded Swashbuckles. Since the only icon type he doesn't do any of is dark, go ahead and equip yourself with the entire set of mage shards. Reverberating Pylonics do shave 10 light icons off of his attacks while dealing a decent dark attack, so that might be worth equipping for a slight edge. Negating Pylonics could save your life (though you should have one on you at all times in the event of emergency scenarios). The best weapon mods for him would be a combination between Blessing of Natural Armor Tears (for a chance of activating a three turn anti-stealing blessing) and Singed Baguettes (for high damage).
Upon defeat, Chase will drop a little bit of sP as well as three items from the following item pool:
Item Hunters Monocle
Item Hunters Sword
Item Hunters Staff
Chases Monocle
Item Hunters Shield
Item Hunters Wand
Item Hunter Crown
Item Hunter Quill
Item Hunter Tiara
Hunters Ring of Stars
Item Hunters Cane-Concealed Dagger
Fire Mage Amulet
Light Mage Amulet
His special loot is as follows:
Item Hunters Smug Waistcoat
Item Hunters Whip
Tome of Fire
Tome of Light
The waistcoat is a wearable and being given two tomes for your hard work getting to win 5 is also nice. Item Hunters Whip is a tier 10 weapon with the following stats:
1-40 light, 1-40 fire
Blocks 75 magma
Low chance of turning a random weapon of your opponent's into a Bag of Sand (3 light; infinite use)
3 mod slots
The whip is a pretty interesting weapon in that although we have several infinite use weapons that have a chance of stealing, this is the only infinite use weapon with a chance of blasting. However, its blasting is not very common and might really only be of use if a battle seems to be getting nowhere. Its attack is very inconsistent (80 icons is a freakishly high amount, but 2 icons just sucks). This weapon can also help you out if you need some magma defense, so it may be of some use to you, especially if your pet cannot yet beat Furious Meatslab or Mutant Scientist.