The collaboration costumes are very nice, but none of them are essential outside of ranking. Eris is the more valuable of the two, you need to max both costumes and get her EX if ranking is your goal. If you can only afford to invest in 1 costume, Master Roxy is the one you'll get the most use out of, but she won't help you rank.

Minimum Banner Recommendations: Tyr
Portrait Costume Summary -1SP Minimum Desired Draw Start Date Last Date
Starlight Guardian Tyr Increase SP cost of abilities by 2 for 6 turns + very strong single-hit 5-tile wide cone (9 tiles) attack. One of the highest damage multipliers in the game, meta material for FH/GR. Note: the debuff has to be up before the ability is reserved to change the SP cost. Recommended - (15 days)
-1SP +1
Min
Goal +5
Pub
General good
FH meta
GR meta
ToS good
LN meta
PvP
Prophetic Dream Darian Very strong single-hit extended X (9 tiles) attack, main target takes 33-50% additional damage. She's a skip/vault, making her challenging to use for general content. Very likely to be meta for FH/GR. Even if you aren't serious about FH/GR, you should get at least 1 copy for her unique push (diagonal pull). Optional - (21 days)
-1SP +1
Min +0
Goal +5
Pub
General
FH good
GR good
ToS
LN meta
PvP maybe
Your Very Own Cat Eris 5-hit attack over 4-tile pyramid, pot increases to 3x2. Main target receives vulnerability to physical, potency increases at +2 and +4. One more hit and 3 less tiles than Young Lady Blade, less damage unless you have elemental advantage. Most desirable MT collab costume. Team 3 material for FH. Optional - (13 days)
-1SP +1
Min +2
Goal +5
Pub
General maybe
FH good
GR
ToS maybe
LN
PvP
Esteemed Adventurer Eris Inverted horseshoe shaped attack (5 tiles), damage nearly doubles when the attack results in 7 or less chains on the target. Excellent damage, but range limits her for general content. Team 3 material for FH. Optional - (13 days)
-1SP +1
Min
Goal +5
Pub
General maybe
FH good
GR
ToS maybe
LN
PvP
Emerging Desire Roxy Weak 3-hit attack over 2 tiles + silence, pot increases range to 3 tiles. The damage is so marginal, most people will tell you there's little point in going beyond +1 if you're not serious about PvP. Optional - (13 days)
-1SP +1
Min
Goal
Pub
General
FH
GR
ToS
LN
PvP good
Respected Master Roxy Single-hit 13-tile diamond, main target takes 50% more damage. Mid damage for the range and SP cost. Outclassed by most 3x3s (including Sword Maiden), only relevant because her competition in water is weak for single-turn clears. Lackluster for multi-turn combat due to weak 2nd costume. Optional - (13 days)
-1SP +1
Min
Goal +5
Pub
General good
FH
GR
ToS good
LN
PvP
Code Name A Rafina Stat reinforcement buff (ATK/Crit, etc.) dispel + weak 4-hit X-shaped attack. Her least used costume. Difficult to use for general content due to range, only used during FH/GR to avoid dead turns and often misses weak tiles. Optional - (14 days)
-1SP +3
Min
Goal
Pub
General
FH niche
GR niche
ToS
LN
PvP